Skip autoscaling test until more reliable

AutoScalingTest has issues which will require rethinking how
this test is implemented, including:
- the optimal ConsumeStopSeconds will depend on the overhead
  of boot time, which varies greatly between bare metal and
  virt-on-virt
- every combination of distro/release/flavor will result in a
  different baseline memory usage, making it difficult to
  determine the ScaleDownThreshold to set

This change skips this test and tracks against the bug:
Partial-Bug: #1257575

Change-Id: I0695a7efacdbeab39c895a97cb45496fcaf97e35
Merge "Skip autoscaling test until more reliable"