Don't actually connect to libvirtd in unit tests.

The libvirt tests shouldn't actually be connecting to libvirtd
while running unit tests. Many of the tests were calling either
getLibVersion or getCapabilites, which would start a connection.
Fake these out so the tests can run properly without libvirtd.

Fixes bug 1157992

Change-Id: Iff1a60fc3cc912fdaf641f1f289744bcc9cc9736
Merge "Don't actually connect to libvirtd in unit tests."