Re-enable 'check_trust_roles'

Re-enable the 'check_trust_roles' method. This can be
merged after the patches for change id
I13ce159cbe9739d4bf5d321fc4bd069245f32734 are merged
(master and stable/icehouse for Keystone).

This changeset updates the new location for the check_trust_role
HTTP status validation (in services/identity/v3/json/identity_client.py).
Previously this was located in identity/admin/v3/test_trusts.py.

Commented code indicating the above location change occurred has been
removed.

Change-Id: If1b7f18d7a357f4b3a4b478e300a17f2cc4a6159
Closes-Bug: #1334368
Merge "Re-enable 'check_trust_roles'"