includes the impersonation object if available in the authentication response
puts the impersonators name and id into appropriate headers if available
removed lingering to-do for impersonation headers
update mock service include impersonate and default region
Adding tests and modifying mock
fixing tests after the rebase
Merge pull request #1127 from rackerlabs/REP-928-Impersonation-V3

Rep 928 impersonation v3