esx: Add vpx:// scheme to allow direct connection to a vCenter

Add a pointer to the primary context of a connection and use it in all
driver functions that don't dependent on the context type. This includes
almost all functions that deal with a virDomianPtr. Therefore, using
a vpx:// connection allows you to perform all the usual domain related
actions like start, destroy, suspend, resume, dumpxml etc.

Some functions that require an explicitly specified ESX server don't work
yet. This includes the host UUID, the hostname, the general node info, the
max vCPU count and the free memory. Also not working yet are migration and
defining new domains.

docs/drvesx.html.in

@@ -4,13 +4,14 @@
     <p>
         The libvirt VMware ESX driver can manage VMware ESX/ESXi 3.5/4.0 and
         VMware GSX 2.0, also called VMware Server 2.0, and possibly later
-        versions.
+        versions. <span class="since">Since 0.8.3</span> the driver can also
+        connect to a VMware vCenter 2.5/4.0 (VPX).
     </p>
 
 
     <h2><a name="prereq">Deployment pre-requisites</a></h2>
     <p>
-        None. Any out-of-the-box installation of ESX/GSX should work. No
+        None. Any out-of-the-box installation of VPX/ESX(i)/GSX should work. No
         preparations are required on the server side, no libvirtd must be
         installed on the ESX server. The driver uses version 2.5 of the remote,
         SOAP based
@@ -27,10 +28,11 @@
         Some example remote connection URIs for the driver are:
     </p>
 <pre>
-esx://example.com                  (ESX over HTTPS)
-gsx://example.com                  (GSX over HTTPS)
-esx://example.com/?transport=http  (ESX over HTTP)
-esx://example.com/?no_verify=1     (ESX over HTTPS, but doesn't verify the server's SSL certificate)
+vpx://example-vcenter.com              (VPX over HTTPS)
+esx://example-esx.com                  (ESX over HTTPS)
+gsx://example-gsx.com                  (GSX over HTTPS)
+esx://example-esx.com/?transport=http  (ESX over HTTP)
+esx://example-esx.com/?no_verify=1     (ESX over HTTPS, but doesn't verify the server's SSL certificate)
 </pre>
     <p>
         <strong>Note</strong>: In contrast to other drivers, the ESX driver is
@@ -43,24 +45,33 @@ esx://example.com/?no_verify=1     (ESX over HTTPS, but doesn't verify the serve
 
     <h3><a name="uriformat">URI Format</a></h3>
     <p>
-        URIs have this general form ('[...]' marks an optional part).
+        URIs have this general form (<code>[...]</code> marks an optional part).
     </p>
 <pre>
 type://[username@]hostname[:port]/[?extraparameters]
 </pre>
     <p>
         The <code>type://</code> is either <code>esx://</code> or
-        <code>gsx://</code> and the driver selects the default port depending
-        on it. For ESX the default HTTPS port is 443, for GSX it is 8333. If
-        the port parameter is given, it overrides the default port.
+        <code>gsx://</code> or <code>vpx://</code> <span class="since">since 0.8.3</span>.
+        The driver selects the default port depending on the <code>type://</code>.
+        For <code>esx://</code> and <code>vpx://</code> the default HTTPS port
+        is 443, for <code>gsx://</code> it is 8333.
+        If the port parameter is given, it overrides the default port.
     </p>
 
 
     <h4>Extra parameters</h4>
     <p>
         Extra parameters can be added to a URI as part of the query string
-        (the part following '?'). The driver understands the extra parameters
-        shown below.
+        (the part following <code>?</code>). A single parameter is formed by a
+        <code>name=value</code> pair. Multiple parameters are separated by
+        <code>&amp;</code>.
+    </p>
+<pre>
+?<span style="color: #E50000">no_verify=1</span>&amp;<span style="color: #00B200">auto_answer=1</span>&amp;<span style="color: #0000E5">proxy=socks://example-proxy.com:23456</span>
+</pre>
+    <p>
+        The driver understands the extra parameters shown below.
     </p>
     <table class="top_table">
         <tr>
@@ -76,8 +87,9 @@ type://[username@]hostname[:port]/[?extraparameters]
                 <code>http</code> or <code>https</code>
             </td>
             <td>
-                Overrides the default HTTPS transport. For ESX the default
-                HTTP port is 80, for GSX it is 8222.
+                Overrides the default HTTPS transport. For <code>esx://</code>
+                and <code>vpx://</code> the default HTTP port is 80, for
+                <code>gsx://</code> it is 8222.
             </td>
         </tr>
         <tr>
@@ -91,6 +103,7 @@ type://[username@]hostname[:port]/[?extraparameters]
                 In order to perform a migration the driver needs to know the
                 VMware vCenter for the ESX server. If set to <code>*</code>,
                 the driver connects to the vCenter known to the ESX server.
+                This paramater in useful when connecting to an ESX server only.
             </td>
         </tr>
         <tr>
@@ -217,7 +230,7 @@ type://[username@]hostname[:port]/[?extraparameters]
         To define a new domain the driver converts the domain XML into a
         VMware VMX file and uploads it to a datastore known to the ESX server.
         Because multiple datastores may be known to an ESX server the driver
-        needs to decide to which datastores the VMX file should be uploaded.
+        needs to decide to which datastore the VMX file should be uploaded.
         The driver deduces this information from the path of the source of the
         first file-based harddisk listed in the domain XML.
     </p>