Update Operation logging to use relayd mechanism

Coming from #64 (closed), once we have aegir:input supporting append mode, we can replace the current Operation logging mechanism (that posts to an http endpoint) with the new relayd/aegir:input mechanism. Once that's done, we can strip out the HTTP endpoints, routes, etc. currently used for this on the Drupal side.

TODO:

• replace HTTP POST in dispatcherd with a relayd task to call aegir:log in append mode
• Handle post-exit-code functionality in a similar fashion
  • drupal aegir:exit-code command
  • relayd post_exitcode task
  • dispatcherd relay_exitcode task
• remove existing HTTP endpoints on Drupal frontend
  • Remove HTTP-based log route (aegir_operation.receive.log.output) and controller
  • Remove HTTP-based exitcode route (aegir_operation.receive.log.exitcode) and controller
• add Operation logging-specific wrappers in dispatcherd and relayd
  • update dispatcherd to replace post to HTTP log route with new aegir_log functionality on relayd
• Remove 'sequence' parameter/base-field see #89