Unit test cases for cinder scripts

Currently, there are no unit tests to test
bin/cinder-{all, api, backup, manage, rtstool, scheduler, volume}.
Adding unit tests for these scripts can help prevent issues similar to
https://review.openstack.org/#/c/79791/ and increase test coverage.

bp unit-test-cases-for-cinder-scripts

Change-Id: I44ff6a8903833c6492a6e91b6d4e24996054eb18