Force types on 'log-size' and 'log-count' arguments for "create-master" command

Previously these arguments were treated as string and passed as strings to
twisted.python.logfile.LogFile.fromFullPath() in buildbot.tac:

rotateLength = '10000000'
maxRotatedFiles = '10'


That led to invalid behaviour of Twisted logger - logs doesn't rotated at all.
Add tests to check correct 'log-size' and 'log-count' formatting
Check only for exception type when checking for Jinja error

Travis version on Jinja has "an integer is required" exception text,
lets not rely on it.
Fix broken scripts.runner tests
Add test for case when "log-count" is None
Remove unused import of 're' module

Strange that pyflakes reported about this only now:
<https://travis-ci.org/vrutsky/buildbot/jobs/14080064>
and doesn't report eralier, e.g.
<https://travis-ci.org/vrutsky/buildbot/jobs/14080076>,
with same pyflakes v0.7.3...
Merge branch 'fix_create_master_log_params' of git://github.com/vrutsky/buildbot