Brocade mechanism driver should be derived from ML2 plugin base class

Change-Id: Iddcb6a43d60d5c9f472912efdecbb2aaa9b7ea4a
Fixes-bug: #1327001
(cherry picked from commit 99840ff808c290bedd4a9832b3ec880e8909412a)
Merge "Brocade mechanism driver should be derived from ML2 plugin base class" into stable/icehouse