Remove pylint errors for undefined GroupException members

Pylint complains about 'SecurityGroupBase' has no 'raise_group_already_exists'
member as these methods are called from SecurityGroupBase but do not exist in
this class. This is fine as this class is not invoked directly. This patch
adds these prototypes which raise NotImplementedError and changes the
inheritance order as to not raise NotImplementedError.

Fixes bug 1138269

Change-Id: I2d7b723a482dc8ca845e52e2a8f44c6fd31fa5db
Merge "Remove pylint errors for undefined GroupException members"