This commit adds the dashboard scenario test to
templates/openstack_tempest_gate.sh.j2 and fixes
tempest_dashboard_login_url and tempest_dashboard_url
since horizon is always configured to use SSL.
The dashboard scenario test involves:
* checking that login page is available
* ability to log in as a regular user
* checking that the home page loads without error
This is a rather simplistic set of tests but will provide valuable
feedback in the gate that we have not introduced any significant
dashboard regressions.
Change-Id: I5c50e30d003080378cc660dda301150b16f45b72
Closes-Bug: #1445368