DHCP agent scheduler support for BigSwitch plugin

Adds support for the Neutron DHCP agent scheduler to the BigSwitch
plugin to support multiple neutron DHCP agents.

Implements: blueprint bsn-dhcp-agent-scheduler
Change-Id: I629ce73c0b97c2409b37afb85639282a116560b7
Remove database section from plugin.ini

Change https://review.openstack.org/#/c/34515 moved the database
config items to neutron.conf but left some commented out
[database] items. Remove them as well.

Closes-Bug: #1247589
Change-Id: I05913d0c27a683cec30cae31a1978612aa1e1360
Remove confusing comment and code for LBaaS

The comment "the driver is optional" is inconsistent with what actually
done. And "vif_driver = None" after raising an exception makes no sense.
So this patch removes these lines.

Change-Id: I7f3d5b6df61037307e952a478f47c59485601847
Merge "Remove confusing comment and code for LBaaS"
Updated from global requirements

Change-Id: I36e3ce085af0b1e9a7dfd91141789fdfbc2049a8
Merge "DHCP agent scheduler support for BigSwitch plugin"
Merge "Updated from global requirements"
Remove the warning for Scheduling Network

when a new port is created, the schedule_network in agentschedulers_db is called.
Since this network may already be hosted, it will directly return None in dhcp_agent_scheduler,
which cause the agentschedulers_db.schedule_network log a warning message.

This is really annoying and making users confused.
And, real warnings are already addressed in the real scheduler function.
which is neutron.scheduler.dhcp_agent_scheduler.ChanceScheduler.schedule by default.

Change-Id: I11bdbe47c2cc0fc45fb143970fb6762678bc27e5
Closes-Bug: #1192786
Merge "Remove database section from plugin.ini"
Merge "Remove the warning for Scheduling Network"
Merge branch 'master' of https://github.com/openstack/neutron into odl_ml2
Add unit tests for OpenDaylight ML2 MechanismDriver

This commit adds some basic unit tests for the ML2 MechanismDriver,
as well as ensuring flake8 passes for all the new code.

Change-Id: I65da9b6bfd9a91a3fdc15ecd8429515eef0bfce1
Cleanup the ODL MechanismDriver

Remove a redundant method, streamline some code.

Change-Id: I0d2b88f226e8ed612b4284689840fab57652da31