Enabled Cisco ML2 driver to use new upstream ncclient

The code is still able to handle the old, custom ncclient that
we used before. It uses the different function signatures
for the ncclient's connect() function to detect which version
is installed.

Change-Id: I09d81b424d86f4cd35ca048507f06471246b91d8
Closes-Bug: 1352635
(cherry picked from commit 74c99fb40d4621c6c0915764537dfb54cc6519ca)
Merge "Enabled Cisco ML2 driver to use new upstream ncclient" into stable/icehouse