Adds an endpoint which will always result in a clobber when accessed by ...

...the client

Some builders are configured in such a way as to always require clobbering,
this is currently acheived by pointing them at the endpoint provided by:
https://github.com/mozilla/build-tools/blob/master/clobberer/always_clobber.php
Which simply returns a lastclobber time of the current time + one hour.
The forceclobber endpoint re-implements this behavior.
it dawns on me that time.time() is not TimeZone specific here, what timezone do we assume, how do we enforce that?  (this issue also exists elsewhere in clobberer as is, so doesn't block this PR but does block clobberer going live)