Comment 19 for bug 1596089

Reviewed: https://review.opencontrail.org/21447
Committed: http://github.org/Juniper/contrail-controller/commit/78e3cdfe2eda73e35abada14a664702ee09a8e2b
Submitter: Zuul
Branch: R3.0

commit 78e3cdfe2eda73e35abada14a664702ee09a8e2b
Author: Nischal Sheth <email address hidden>
Date: Sun Jun 26 00:35:22 2016 -0700

Use separate task for IFMap DB

In scaled setups it was observed that running the graph walker stalled
bgp/xmpp peer join/leave processing. This happens because graph walker
runs in db::DBTable task, which is exclusive with bgp::PeerMembership.
Since bgp::PeerMembership cannot run when graph walker is running, peer
join/leave processing gets delayed as well.

Address this by running all the IFMap server side code that used to run
under db::DBTable in a new db::IFMapTable task.

Following changes are implemented:

- Update DB infra to use a user specified task for a given DB, with the
default task as db::DBTable.
- Eliminate use of static members to store task ids so that different DB
instances can use different tasks.
- Fix production and test code to initialize config DB with new task.

Note that agent IFMap code is unchanged.

Change-Id: Id30c89840690e8f41ebf3b277eaedb150c09d123
Partial-Bug: 1596089