Add support for schema validation when passing in XML

The virDomainDefineXMLFlags and virDomainCreateXML APIs both
gain new flags allowing them to be told to validate XML.
This updates all the drivers to turn on validation in the
XML parser when the flags are set

include/libvirt/libvirt-domain.h

@@ -273,6 +273,7 @@ typedef enum {
     VIR_DOMAIN_START_AUTODESTROY  = 1 << 1, /* Automatically kill guest when virConnectPtr is closed */
     VIR_DOMAIN_START_BYPASS_CACHE = 1 << 2, /* Avoid file system cache pollution */
     VIR_DOMAIN_START_FORCE_BOOT   = 1 << 3, /* Boot, discarding any managed save */
+    VIR_DOMAIN_START_VALIDATE     = 1 << 4, /* Validate the XML document against schema */
 } virDomainCreateFlags;
 
 
@@ -1417,6 +1418,10 @@ int                     virDomainMemoryPeek (virDomainPtr dom,
                                              void *buffer,
                                              unsigned int flags);
 
+typedef enum {
+    VIR_DOMAIN_DEFINE_VALIDATE = (1 << 0), /* Validate the XML document against schema */
+} virDomainDefineFlags;
+
 /*
  * defined but not running domains
  */