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

Usefull after fork.

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

Uses a fork and permits to set ionice on child.

/!\ Don't use logging for logging as it would (maybe) end in a deadlock for the
child.

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.