horizon replaced nodejs by a python alternative

since commit a0739c9423a4c559b45af96fa4cdb30539dcdbd7 and the Havana
release, horizon uses a pure Python alternative to nodejs.

Horizon changed the way to use the compress utility, the option
offline_compress is no longer available.
Thanks to Maxime Vidori for the information.

Change-Id: Ie290701b00c97352838e13182b940a6de46a591f
(cherry picked from commit fae0d04b82867dab3c355e5f1d5a9b2d0054f949)
Introduce keystone_url parameter

This parameter deprecates keystone_host, keystone_port & keystone_scheme
and allows to pass a complete url.

Implements blueprint serve-keystone-from-wsgi

Change-Id: Ia8aa6e6377abf0e84427174fb946f4efa5defa12
(cherry picked from commit 314df2136eb54ac95d0716d00f20265c5c439494)
Merge "horizon replaced nodejs by a python alternative" into stable/havana
Merge "Introduce keystone_url parameter" into stable/havana