Move sahara client installation to lib/sahara

All other projects installs their clients in the same lib file as the
main services.

Remove sahara-dashboard installation

Sahara dashboard is now merged into the Horizon and enabled by default
(when data_processing endpoint is available), so, we should stop
installing it as separated dashboard.

Change-Id: I1f0e93e1dee3d065c4f00d8bf2042bebc8d45a22
Merge branch 'master' of https://github.com/openstack-dev/devstack