As described in the spec there is no need to explicitly bind
DVR router to each l3 agent running on compute nodes where
there are dvr serviceable ports - this brings complexity to the code,
makes it less readable and very hard to maintain (one could see how many
bugs were filed and fixed regarding dvr scheduling stuff already).
Also this brings scalability problems as time needed for router scheduling
grows linearly with the number of compute nodes.
The idea is to align dvr scheduling with legacy router scheduling:
only schedule SNAT portion of the router and use DB queries whenever
we need to know which compute nodes should host the router.
Implements blueprint improve-dvr-l3-agent-binding
Change-Id: I82c8d256c56bb16cdc1b1232ebb660d09909f9c6
0496f95a13