Remove "#!/usr/bin/env python" from .py files under nova/cmd

Fix bug 1178543

Now in Havana, all nova service script start up logic are moved to
nova/cmd and those files are not simply python script but python
files, so there is no need to still keep "#!/usr/bin/env python"
for those files since they won't be run directly as scripts.

Change-Id: Ic102215dc0200ec1f6b47951bef31d58b08022ef
Use Oslo's `bool_from_string`

Oslo provides an equivalent implmentation of `bool_from_str` so we
should switch the code to use that instead.

Change-Id: I382f23af2468e276ae4342dff18cf06e1c24b755
Merge "Remove "#!/usr/bin/env python" from .py files under nova/cmd"
Merge "Use Oslo's `bool_from_string`"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp