Drop autoscaling scenario test

Drop autoscaling scenario test. It has always been skipped, so there
is no loss of test coverage. It takes a very long time to run since
it uses real alarms to perform 4 scaling operations.

See https://review.openstack.org/#/c/122320/.

Change-Id: If37f63565a235c6128566f8f2cd993ed247f0912
Partially-implements: bp/tempest-client-scenarios
Merge "Drop autoscaling scenario test"