Create new Geo scenario to test a live Geo instance

Currently there is one Geo scenario that first orchestrates a Geo instance, then runs the tests.

This MR adds a new scenario similar to Scenario::Test::Instance::Any, in that it accepts the addresses of already-live Geo nodes, then runs the tests.

This scenario was created so we could runs Geo tests against a live instance using the Gitlab QA gem.

The MR also adds support for environment variable GITLAB_QA_LOOP_RUNNER_MINUTES, which is related to these recent changes: https://gitlab.com/gitlab-org/gitlab-qa/merge_requests/300 and https://gitlab.com/gitlab-org/gitlab/merge_requests/18546

Both of these changes are related to https://gitlab.com/gitlab-org/quality/testcases/issues/194

Closes #424 (closed)