In function _raise_contrail_exception, exceptions.BadRequest is used
instead of 'BadRequest' as a string

This bug is introduced because of this https://review.opencontrail.org/#/c/2568/

Change-Id: I8900387b16630e72dcf07c4827f13d772b20175c
Closes-bug: #1368536
Merge "In function _raise_contrail_exception, exceptions.BadRequest is used instead of 'BadRequest' as a string"