Remove extraenous instantiations of managers

There were cases where a number of the API managers were being
instantiated more than one time. This could cause a number of
odd edge cases where the managers would have different
configurations and/or different dependency injection results.

The managers should now be properly instantiated only once
unless explicitly required (e.g. testing the token provider
manager raises an exception in badly configured states).

Conflicts:
	keystone/auth/plugins/token.py

Closes-Bug: #1294994
Change-Id: I1babb065065cb5b06899f59568020a1c38f1156c
(cherry-picked from commit 0a1cb0e20247a3c7856b409452b01ad6db8069f0)
Merge "Remove extraenous instantiations of managers" into stable/icehouse