Handle unicode at the caching layer more elegantly
Handle unicode at the caching layer more elegantly

This patchset resolves an issue where in some cases unicode would
cause the cache key generator to raise a UnicodeEncodeError due to
the name/value being outside of the standard ascii character set.
Included is a fix to the cache backend debug code to utilize repr
for passing the keys/values to the logger.

Tests in test_backend provided by chenxiao <chenxiao@cn.ibm.com>

Closes-bug: 1237892
Change-Id: I4df1c9eb6b4a1367defdbb6bcbcd1f1f992348e5

openstack/oslo.cache,citrix-openstack-build/oslo.cache,openstack/oslo.cache