Separate upgrade logic to is_upgrade job var and rename
scenarios to match.

Rename "ACTION" to "SCENARIO" (as it is a scenario).

Separate testing of dashboard (aka Horizon) and increase
its timeout to 5 minutes (CentOS 7 slow as always).

Separate initialization of core OpenStack.

Use gate setup script from ./tests/

Remove useless tox setupenv.

Do not deploy Heat when not really necessary.

Change-Id: I4fca319ccc3de7188f8b7b44c9c71321e3899467