Modify midonet plugin to support the latest MidoNet

MidoNet has been upgraded and devstack needs to be updated to
be compatible.  This change is required to run the current
version of MidoNet plugin with DevStack.

Closes-Bug: #1222314
Change-Id: If3379b4d5da4e4fcf989ee7398b5952d71b68d5a
Merge "Modify midonet plugin to support the latest MidoNet"