Improve savanna-dashboard installation

* split configurations setting to one-per-line;
* don't set SAVANNA_URL in horizon configs - we're now using endpoits
  keystone to find corresponding edpoint.

Change-Id: I9497a511656a2f70e923b651c66c5ef2917a0939
Merge "Improve savanna-dashboard installation"
Merge branch 'master' of https://github.com/openstack-dev/devstack