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.
Add the option to retry spot requests if they were rejected with
price-too-low.
Fix pep8.
Fix more pep8.
Add explicit reset of spot price. Document recent changes.
Merge remote-tracking branch 'upstream/master'
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.
add a poll.method decorator
remove unnecessary SerializedInvocation
remove PollingChangeSource docstrings
Fix poller hook

This is still not appropriate for nine.  Rather than forcing local
change sources, it should be sending a message to force remote change
sources.  But, good enough for the moment.
Added unit test for ticket auth in P4 source step.
Add a unit test for ticket auth in P4 poller.
Modularize plugins
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.