Fix reading cache-time before configured

There were several places where the cache time was read at
import-time. This means that the default value is used rather
than the value that the user configured because CONF() had not
been called yet.

This change makes it so the values are read at run-time, after
CONF() has been called.

Change-Id: I835418f249c5217bf79efebad1dee22d25f6774a
Closes-Bug: #1265670
Don't configure on import

The keystone.config package called config.configure() at import-
time.

This will make it obvious that developers can't use config
options at import-time because packages that do that will fail on
import.

Change-Id: I9306f67609d782e3f49fd43908448daf1287d51c
Related-Bug: #1265108
Related-Bug: #1265670
Closes-Bug: #1269785
Merge "Fix reading cache-time before configured"
Merge "Don't configure on import"