Test force_config_drive as a boolean as last resort

The force_config_drive help clearly states that only possible option is
'always' but folks are setting it to 'True'/'False' etc and expecting
it to work. So let's enable that as well. In the worst case scenario
mentioned in the bug, it was set to 'False' and since the check for
force_config_drive took any string as true, we were enabling the flag
to true. With the change in this review, we force a conversion of the
string to true. Additional check for the flag to be set as 'always' is
treated as true as well. The test case checks for all the variations

Closes-Bug: #1319180
DocImpact

Change-Id: Ifa6348fa7dfd9de063eb13d30e3ddf94fa530b57
Merge "Test force_config_drive as a boolean as last resort"