Logging service check

When any service has a syslog_drain_url, it has to 'require' syslog_drain. 

This is to prevent a security issue. If a service provides a syslog_drain_url, loggregator will forward all messages automatically to that service. Therefore, a service has to announce itself as a syslog service for a bind to be successful, if it provides a syslog_drain_url.

See here: https://www.pivotaltracker.com/story/show/56720664

-- Signed off by Johannes Tuchscherer