moves default keystone API to v3

v2.0 of the keystone API was deprecated in icehouse-2, moving to
support v3 by default.

This also fixes a bug in Horizon where if you specify v3 for the
API version and v2.0 is still the auth url, login fails.

Implements blueprint keystone-v3-default
Partial-bug: #1267636

Change-Id: Ibc4872f24125fa74230eab781b002dffdba5f5da
Merge "moves default keystone API to v3"