Add port bindings to ports created in Midonet

Currently Midokura uses its own script (mm-ctl) to bind ports. However, support
for using this script is left out of the nova and neutron projects. This causes
confusion and makes deployments unnecessarily complicated for customers using
Havana. This fix is to change Neutron to properly set up port bindings to use
the "midonet" vif driver when creating a port. Corresponding changes will be
submitted to the devstack and Nova projects.

Change-Id: I91f2e4fe7135da0c22fb408081efdc63fff748df
Closes-Bug: 1235134
Merge "Add port bindings to ports created in Midonet"