EC2 client token is not reuseable for new instance creation

According to the Amazon documentation the the token is not reuseable
 for NEW instance creation at least for 24h.
Removing the new instance creation part from the
 test_run_idempotent_instances.

This change will allow as to fix/workaround the ec2 image bundling issue
 at devstack/euca2ools/boto side.

Change-Id: Id6eeeac303a31d69060ca454a5e224405229a39e
Merge "EC2 client token is not reuseable for new instance creation"