Ensure JSON headers in Auth Requests

The Content-Type header will be set automatically by the request call
however we should also ensure that we set the Accept header because our
auth plugins only work with JSON.

Change-Id: Ib3badd70f4fa32d400565c39a072db547d86037e
Use `HttpNotImplemented` in `tests.v3.test_trusts`

Since we are moved to usage exceptions from oslo, `HTTPNotImplemented`
was renamed to `HttpNotImplemented`, so we need to change usage of this
exception in tests.

Related to blueprint common-client-library-2

Change-Id: I51f6593ebb86267dad7086d4862a135743f2de7f
Updated from global requirements

Change-Id: Icc5f3cdf0cfe9a1566ff5efafc85471381e3622d
Merge "Use `HttpNotImplemented` in `tests.v3.test_trusts`"
Merge "Ensure JSON headers in Auth Requests"
Merge "Updated from global requirements"