Ensure logger level is always non-nil

Rails 4.1 dies terribly if the logger level is set to nil.
Merge branch 'rails41' (tests) into redcanaryco-rails4.1-logger-fix

Adjust lib/health_check/health_check_controller.rb to check if @old_logger_level is set
Merge branch 'rails41' into redcanaryco-rails4.1-logger-fix
Merge branch 'redcanaryco-rails4.1-logger-fix' into rails41