ofagent: bye bye br-tun

WIP

Implements: blueprint ofagent-merge-bridges
Change-Id: I21ee1c6d141863182b487e10c7bfe911b1a472ab
ofa_neutron_agent: l2pop_network_types

Change-Id: I2f200a1ae2bd769ea1f83fe65e58e82325ed92b0
some fixes

Change-Id: I9f271753e5a2492cc0269a6d413a49ea6f77a331
some fixes

Change-Id: Ib322063e04f0f9b283ccf39673734a8e65761ce3
some fixes and cleanup

Change-Id: Ib591c2c45c9ffec2711102f2de593b6dc1ad190b