fixed typo
check --db parameter for 'buildbot create-master' command

Check that database URL specified via --db parameter is valid. Print
usage error otherwise.
fix and enable empty-docstring (C0112) pylint check
BaseBasicScheduler: fix typo
Merge pull request #881 from lewurm/typo

BaseBasicScheduler: fix typo
Merge branch 'create-master-db-arg' of git://github.com/elmirjagudin/buildbot
Merge pull request #874 from elmirjagudin/pylint-empty-docstring

fix and enable empty-docstring (C0112) pylint check