Add support for custom libvirt uri

SSH driver executes "virsh list --all" without setting the default
libvirt uri. It can cause issues eg. on Fedora where the default uri is
"qemu:///session" instead of "qemu:///system" and as a result it doesn't
find any domain. This patch adds support for setting libvirt uri.

Change-Id: If714913c8b41097f25026afabbb88aa90c496d81
Closes-bug: #1281025
Merge "Add support for custom libvirt uri"