Metaclass Python 3.x Compatibility

According to the OpenStack style guide
(http://docs.openstack.org/developer/hacking/),
for Python 3.x compatibility use "six.add_metaclass"
instead of " __metaclass__."

Closes-Bug: #1236648
Change-Id: I2f507a90ee08cc05bd764549002a4656c187b6fc
NSX: get rid of the last Nicira/NVP bits

These were kept for bw compatibility in Icehouse, but
these are removed in Juno.

The king is dead, long live the king!

DocImpact
Blueprint: nicira-plugin-renaming

Change-Id: I49d19fec90ba191ed5b895fac8a884070f52119e
Merge "NSX: get rid of the last Nicira/NVP bits"
Merge "Metaclass Python 3.x Compatibility"