IF both service neutron-l3-agent and neutron-server are up,
but no router id configured in /etc/neutron/l3_agent.ini, an
exception will be raised on DB as "DBError: IntegrityError",
because the variable router_ids has a default '' value that
doesn't match the DB grammar.
* Check router id is specified in _init_() of l3 when
not using namespace.
* Move part of checking config params actions to new function
_check_config_params()
* Add corresponding unit tests.
Closes-Bug: #1226366
Change-Id: I905f8a4061c5b250782e025681dfefcc41c8c03c
96e0eb23a4