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