Add misssing yield
Fix a bug with timestamp handling in the IMPI cache
Make the cache object return None on a cache miss rather than throwing NotFoundException
Merge branch 'dev_new_homestead_api' of github.com:Metaswitch/crest into dev_new_homestead_api
Merge remote-tracking branch 'origin/dev_new_homestead_api' into homestead_overload
Update import
Merge remote-tracking branch 'origin/dev_new_homestead_api' into homestead_overload
Test updates