Bump minimum requirement for dogpile.cache

Move the minimum requirement for dogpile.cache to 0.5.3 for py3k
compatibility fix (on .get_multi() ) and general quality of life
fixes for interacting with the region objects (.is_configured
instead of a try/except or if 'backend' in __dict__).

Change-Id: I21cff58726997f5c6564e9b66520c9c51802fe3b
Merge "Bump minimum requirement for dogpile.cache"