Tests added for glance/cmd/cache_pruner.py

Related to blueprint glance-cmd+unittests

Integration test test_cache_pruner_main added to cover
chain of calls between glance/cmd/cache_pruner.py and glance/image_cache
module.
Unit test test_cache_pruner_main_runtime_exception_handling added to
cover exception handling for main() method of cache_pruner.py

Change-Id: I7d7b182260a407aed1288a5d136e03cbe029523f
Sync gettextutils from Oslo

Sync the latest code from Oslo to support Glance i18n.

afdbc0a Fix E501 in individual openstack projects
9d529dd Make Message keep string interpolation args
ec6d900 Add support for locales missing from babel
221c37d Allow the Message class to have non-English default locales
0e1af5b Implementation of translation log handler
2cfc1a7 Translation Message improvements

Partially implements bp i18n-messages

Change-Id: Ia56a94e42ebe1d9b539b7bc513b0342e9b2450b3
Merge "Tests added for glance/cmd/cache_pruner.py"
Merge "Sync gettextutils from Oslo"