Added first version of osprofiler support.
Added for all nb_db classes, for all events and first_packet handling in
the controller.
See osprofiler guide at:
https://docs.openstack.org/zaqar/latest/admin/OSprofiler.html
Dragonflow instructions are at doc/source/osprofiler.rst.
Change-Id: I2ad3405f6884d6a39f243913c1ab5bdaf6855b84
Closes-Bug: #1690272