GerritStatusPush: Fix labels with gerrit >=2.6

Fixes #2550. Gerrit versions 2.6 and newer do not accept the
--verified option if the Verified label does not exist in All-Projects
in the gerrit configuration. Instead, we must give the --label option.
So, use --label for --verified and --code-review so we can work with
all gerrit installations.

While the --code-review option does still work, so does the --label
approach. It seems more likely that --label is more likely to work in
the future than --code-review, so we'll just go with the safer route.

In order to still support older gerrit installations (which do not
support the --label option), query the gerrit installation version
whenever we submit a review. Cache this version query for 10 minutes,
so we do not ask the gerrit server every single time for its version.
added BitbucketPullrequestPoller changes source

The BitbucketPullrequestPoller polls a Bitbucket repository (merucrial
or git) for new or updated pull requests.

* master/buildbot/changes/bitbucket.py: added
added BitbucketPullrequestPoller tests
BitbucketPullrequestPoller unittests fixed pep8 issues
Support tagging instances after they have launched.
add some unit tests for EC2LatentBuildSlave
make botoSetup return connection
don't call create_tags unecessarily
test start_instance with tags
document tags parameter for EC2LatentBuildSlave
skip ec2 buildslave tests if moto not found
remove moto dependency from setup.py
skip ec2 buildslave tests if moto version is not up to date
add lost comma to setup.py
Parameterize ForceScheduler button name
Documented the 'project' paramter to P4Source.
Changed the description about project parameter
Un-Revert and put back: "Merge branch 'SlaveInfo' of git://github.com/jaredgrubb/buildbot""

This reverts commit f518276b3a6e88a6b079a4e2661a152087eedd15.

Conflicts:
	master/buildbot/test/unit/test_buildslave_base.py
SetSlaveInfo: fix bug in implemenation
Add the 'slave info' table to the buildslave web page