openstack backup methods and theirs helpers (itacloud-2671)
instance backup strategy and its tests(itacloud-2671)
instance backup strategy entry point (itacloud-2671)
entry points logic implemented in backups app (itacloud-2671)
openstack restore_instance method corrected (itacloud-2671)
backup strategy removed from iaas models (itacloud-2671)
backup unittests were moved to separate folder
test_scenarios separated to 2 files (itacloud-2671)
commands tests were rewritten (itacloud-2671)
ordereddict added to requirements (itacloud-2671)
polling command was removed and logic was rewritten to avoid polling (itacloud-2671)
added erred method to backup model (itacloud-2671)
merge with current develop (itacloud-2671)
Change example of a native name to fix sphinx pdf
Expand caught error types
Merge branch 'feature/itacloud-2811-2' into 'develop'

Feature/itacloud 2811 - crf
Merge branch 'feature/itacloud-2671' into 'develop'

Feature/itacloud 2671

1. Code from https://github.com/djyoda/openstack-backup-restore was adapted and moved to openstack backend.
2. Added instance backup strategy.
3. Added entry point for instance backup strategy.
4. Added entry points usage in backup app.
5. Poll command and polling logic removed. Now backup state changes in tasks.