Replaced all logger call in child.
Added dedicated libev loop.
Handle exceptions using fatal helpers of ForkedJob.

Replace logging calls with sys.stderr.write in order to prevent deadlock in the
fork.

Indicates if driver used for disk backing is using some sort of caching which
may lead to data corruption for a live migration.

This prevents client libvirt version 0.8.8 to segfault when reseting libvirt
event handlers.

sending events on removed domains or sending removed event too late.

Sometimes, libvirt tells us too late that a domain has been removed.

This is a fix when is the same poll we try to update a tag value for a VM and
the domain just has been removed.

Needed for disk synchronisation during live migration.