P4 source changes:

* Made `mode` parameter support property interpolation
* Added ticket-based authentication
Added support for ticket-based authentication to P4Poller.
Added ticket login interval to P4Poller.
Some code cleanup.
P4Poller: fix ticket-based authentication, add optional debug logging.
Default P4Poller's ticket fetching interval to 24 hours.
Updated documentation and release notes about support for Perforce ticket-based authentication.
Added unit test for ticket auth in P4 source step.
Add a unit test for ticket auth in P4 poller.
use pylint symbolic check names

In pylint configuration replaced check numbers with
check's symbolic names. It seems that check numbers are
on the way to be depricated.
enable more pylint checks

Trimmed the disabled pylint checks list, by removing checks
that are passing now.
fix sqlalchemy statement

sqlalchemy use immutable objects, so we must do q=q.where..

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
Merge ludovicchabant/buildbot:perforce (PR #1128)

Conflicts:
	master/buildbot/changes/p4poller.py
	master/buildbot/test/unit/test_changes_p4poller.py
	master/buildbot/test/unit/test_steps_source_p4.py
	master/docs/relnotes/index.rst

+ autopep8
+ substantial merging in tests
Merge branch 'master' into nine

Conflicts:
	master/buildbot/changes/p4poller.py
	master/buildbot/test/unit/test_changes_p4poller.py
Merge elmirjagudin/buildbot:pylint-conf (PR #1161)