stop indexing libvirt logs

We need a much higher level of output on libvirt logs to get to the
bottom of Bug 1254872. However, at that level of output, we crush
elastic search. So turn off indexing this log in the gate until we
get to the bottom of the bug and can return it to a more reasonable
logging level.

Change-Id: I9fec939883e50b421bc0530205e8b0bd7eab2350
Related-Bug: #1254872