Fixes LP#920812 - KeyError: 'overLimit' on 413 return

Turns out that over quota limit and over ratelimits
return different keys in the faults. This patch adds
a new exception for RateLimitExceeded that handles
413 returns when there is an overLimitFault key (and
not the overLimit key that is in the over Quota fault)

Change-Id: I64d10cb592512e7de71c5d8518131deee516d9b2
2 files changed