network: put dnsmasq parameters in conf-file instead of command line

This patch changes how parameters are passed to dnsmasq.  Instead of
being on the command line, the parameters are put into a file (one
parameter per line) and a commandline --conf-file= specifies the
location of the file.  The file is located in the same directory as
the leases file.

Putting the dnsmasq parameters into a configuration file
allows them to be examined and more easily understood than
examining the command lines displayed by "ps ax".  This is
especially true when a number of networks have been started.

When the use of dnsmasq was originally done, the required command line
was simple, but it has gotten more complicated over time and will
likely become even more complicated in the future.

Note: The test conf files have all been renamed .conf instead of
.argv, and tests/networkxml2xmlargvdata was moved to
tests/networkxml2xmlconfdata.

tests/networkxml2confdata/dhcp6host-routed-network.xml

@@ -0,0 +1,19 @@
+<network>
+  <name>local</name>
+  <uuid>81ff0d90-c91e-6742-64da-4a736edb9a9b</uuid>
+  <forward dev='eth1' mode='route'/>
+  <bridge name='virbr1' stp='on' delay='0' />
+  <mac address='12:34:56:78:9A:BC'/>
+  <ip address='192.168.122.1' netmask='255.255.255.0'>
+    <dhcp>
+      <host mac='00:16:3e:77:e2:ed' name='a.example.com' ip='192.168.122.10' />
+      <host mac='00:16:3e:3e:a9:1a' name='b.example.com' ip='192.168.122.11' />
+    </dhcp>
+  </ip>
+  <ip family='ipv6' address='2001:db8:ac10:fd01::1' prefix='64'>
+    <dhcp>
+      <host name='ralph' ip='2001:db8:ac10:fd01::1:20' />
+      <host name='paul' ip='2001:db8:ac10:fd01::1:21' />
+    </dhcp>
+  </ip>
+</network>