Attempt to break the pid lock during startup.

This commit attempts to break the pidfilelock during startup in cases where the
process may have exited without successfully cleaning up the lockfile. It also
attempts to grab the lock before opening the context. Also applied to the
Collector module, which may have been looking for the wrong exception since it
does not rely on a timeout.
pylint fixes.
Fixes to ensure pidfile can be opened or broken if stale.
Catch possible typeerror resulting from None being returned when reading the pid.
Remove PIDFileError as it does not always exist in the package and is rarely used.
Merge branch 'cleanup_pidfile' of https://github.com/mattikus/bcfg2 into maint