This commit includes new unit tests for subcloud_manager.py,
covering new test cases in deploy, backup, migrate, install,
rename operations.
Test plan:
1) PASS: Run tox py39, pylint and pep8 envs and
verify that they are all passing.
2) PASS: Check 'tox -e cover' command output.
Coverage increased from 79% to 90%
Depends-On: https://review.opendev.org/c/starlingx/distcloud/+/914075
Story: 2007082
Task: 49618
Change-Id: I1219ce7c5f6cebc0d1cb564905eb5cc5b4045540
Signed-off-by: Swapna Gorre <swapna.gorre@windriver.com>