Fix/kvm qmpbackup 0.42
- 
upgrade to qmpbackup 0.42+  - 
cover empty backup recovery  - 
assert virtual.qcow2.gz removal on backup  - 
assert presence of Post take-over cleanup after take-over  - 
split TestInstanceResilientBackupExporterto assert one per one - 
https://github.com/abbbi/qmpbackup/issues/18