Policy Enforcer, pass entire context dict

The oslo enforcer expects "as much detail as possible" about the
calling user in the creds dict, so include the whole context dict,
which will enable more complex policy rules to be expressed than
with the current code where we pass only a subset of the context
data.

Change-Id: I70bd0fb07bb0b8e9c3c2b94b399197ad207d0fd2
Merge "Policy Enforcer, pass entire context dict"