HA failover testing requires the ability for two L3 agents to
co-exist on the same machine. The following changes were made
to support this:
* Add l3 agent ability to simulate nested namespaces by suffixing
each router namespace with '@host'. For example, if a router
with id '1' is created, its namespace will be:
* Added test.common submodule which will hold common code which is
shared between the different kind of tests (unit and funtional).
* Added tests.common.agents submodule which holds test-only agents, and
added a test L3NAT agent to be used in the HA functional testings.
Co-Authored-By: Assaf Muller <firstname.lastname@example.org>