Fix issue related to bytes (py3) and str (py2) while running magnum
cluster-config/bay-config command.
Also increate code coverage for cluster_shell and bay_shell to 92%.
Overall code coverage now is 75%
Closes-Bug: #1649192
Partially implements: blueprint magnumclient-ut-coverage
Change-Id: I99610eea1e1e24f187baf1bd03c7e4e5a337bc7d