refactor: dashboard tests
refactor: dashboard tests

those tests were creating and stopping one service each.
that's not a reasonable thing to do if those are costly operations.
we now do a single start and stop and verify the dashboard statistics all in one
go, which also speeds up the test by... A LOT!

dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui