Use common create_keypair method for autoscaling

The scenario test for autoscaling was implemented at the same time
with cleanup patch of create_keypair methods, and the cleanup patch
could not cover autoscaling test.
This patch covers autoscaling test.

Change-Id: Ibf4e98a9d4616c1dc6d2f08bde3d04a40b910067
Merge "Use common create_keypair method for autoscaling"