Initial Trusts support

Implements client support for the basic trusts API operations,
note this does not include support for the roles subpath operations,
support for those can be added in a subsequent patch.

Change-Id: I0c6ba12bad5cc8f3f10697d2a3dcf4f3be8c7ece
blueprint: delegation-impersonation-support
Restore client.py for backward compatibility

Simply pull in HTTPClient from its new location. This also restores the
tests that were modified back to there original form to make sure
nothing has changed from the original.

Fixes: bug 1211998
Change-Id: Ia3241a4352eb6b37c6489cd4dd1bc373de107e12
Merge "Restore client.py for backward compatibility"
Merge "Initial Trusts support"