Fix undefined variable in cache

A function to verify metadata in the cache middleware was falling over
for GETs on images with a missing size.

Fixes bug 1183049

Change-Id: I2da75e5e5aca12d20a10cace2a3779e4041161b2
Sync oslo imports to the latest version.

Change-Id: I36193d00930e5c82c46841b64650863c811b95a4
Import strutils from oslo, and convert to it.

The only change of behaviour here (according to the former glance
unit tests) is that 'T' now means True not False. I suspect that's
ok.

Change-Id: Icf98f913a3f78a1fe2f38a82a25a071c2da03739
Merge "Sync oslo imports to the latest version."
Merge "Import strutils from oslo, and convert to it."
Merge "Fix undefined variable in cache"