Improves UT coverage for dcmanager's manager/service.py
from 72% to 92%
Test plan:
1) PASS: Run tox py39, pylint and pep8 envs and
verify that they are all passing.
2) PASS: 'tox -e cover' command output is 92%
Story: 2007082
Task: 49605
Change-Id: I72a361bf89d3df32f71e78e16e107b183974c53e
Signed-off-by: Swapna Gorre <swapna.gorre@windriver.com>