Add maintenance script for the API cache

Replace cache entry deletion in TestRequest with a new
script 'cache.py' which reports cache entries with a password
and allows them to be fixed.

cache.py also allows cache entries to be queried and deleted
based on other conditions.

Change-Id: I727af9b6fa10d2231e5d777a1bc6f8602ca03f50
Merge "Add maintenance script for the API cache"