Remove List events API from Cisco N1kv Neutron

Earlier Cisco N1kv plugin was using list events api to
poll policies from VSM.
It was inefficient and caused delay in processing.
So, now Cisco N1kv plugin  switched to list profiles to
poll policies from VSM.

Change-Id: Ia734735361dc3eaee8e276ada0c80045eaa9ef96
Closes-Bug: #1292173
Re-submit "ML2 plugin should not delete ports on subnet deletion"

This patch was previously merged:

Commit: 0d131ff0e9964cb6a65f64809270f9d597c2d5d1

And reverted by this commit da00ed76e6008bd06dada0f0441ae436dd759cdf
in order to check if there was a relation with the gate failures.

Change-Id: Iacb4de8d9aa6a6cbe32c4f41fcf2657f2d09e6e2
Merge "Remove List events API from Cisco N1kv Neutron"
Merge "Re-submit "ML2 plugin should not delete ports on subnet deletion""