Try base InstanceSetParams tests that modify instance's
devices with hotplug=True.

Add some unittests for kvm hypervisor regarding runtime file
manipulation. Based on a sample runtime file search for
specific disk and nic entries based on their UUID.

Add unittest for kvm device id generation.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Signed-off-by: Thomas Thrainer <thomasth@google.com>
Reviewed-by: Thomas Thrainer <thomasth@google.com>