...and pin us to stable/newton. (I wanted stable/mitaka so it'd match
Keystone, but apparently then pbr is too old for Keystone to install
a keystone-wsgi-admin script.)
This prevents various version conflicts; the most recent was from
oslo.service blocking too-new eventlet.
Change-Id: I115dc231a9156a5bceacaa21d6242bb934fbbd24
Related-Change: I3b2196fdef9936f1c7d468f9c7c9b9246d3d26fd
Related-Change: I6cbbfd7260571f42ea65c6622aa6b410a0e43b28
397ed3ab6a