Make it possible to use horizon for backing
up snapshots.
* Add snapshot column to backups table
* Add snapshot information to backup detail
* Fix wrong template path in create_backup.html
* Add ChoiceField with snapshots belonging
to the volume in create backup form
* Add create backup option in snapshots table
* Adjust tests and test data
When backing up from snapshots table the snapshot
ChoiceField is preset with the choosen snapshot
as the only option.
Implements: blueprint volume-snapshot-backups
Change-Id: I4b7707d95756501e0622460e3ddc4e3f7624f02e
9fa1cddf09