Detect and correct invalid libvirt plugin caches
Detect and correct invalid libvirt plugin caches

It has been reported that a libvirt cache file may become corrupt,
having 0 bytes and causing TypeErrors as the YAML is invalid.

This change detects invalid structure of the caches and rebuilds them
if necessary.

Change-Id: Ie0a7286123a413b3c074f1cd8c1c2cf62cfe4ac0

sapcc/monasca-agent,sapcc/monasca-agent,sapcc/monasca-agent