Snapshots glance and blockstorage changes

* New tests for V1 boot from volume snapshot scenarios
* Fixes in V2 snapshots scenarios
* PEP8 fixes
* Added extra lines and remove assignment to local variable as not needed

Change-Id: Ia640085a3ed0e3c3935b6a6d3f19402e5b62a574
Merge "Snapshots glance and blockstorage changes"