Remove time formatting in agent clock error

Remove time formatting in agent clock error

This removes time formatting that may be hiding timezone
issues that are leading to a delta being calculated between
the agent and the server even when it shows none. It also
adds logging of the difference so we can see how far off it
thinks they are.

Example message:
during the registration of Open vSwitch agent has a timestamp:
2015-05-19T18:15:27Z. This differs from the current server
timestamp: 2015-05-19T18:15:27Z by more than the threshold agent
downtime: 75.

Note that the timestamps are exactly the same after formatting.

Change-Id: Ibfc30444b7a167fb18ae9051a775266236d4ecce
Related-Bug: #1456760