Libvirt: call capabilites before getVersion()

Updates the Nova libvirt driver so we make a call to get
the driver capabilities. This is clearly a work around
but it does allow nova-compute to startup cleanly when
performing a clean install of Fedora 19.

See notes in: https://bugzilla.redhat.com/show_bug.cgi?id=1000116

Fixes LP Bug #1215593.

Change-Id: I2c74dc001032e3cc4d7d55a3fa407b96fd0d0e78
Merge "Libvirt: call capabilites before getVersion()"