Rather than rely on or work around JRE behavior based, lock S3ClientMockTest using OkHttp.
JCLOUDS-49 clear remaining async stuff from openstack
JCLOUDS-150 clear remaining async stuff from aws
JCLOUDS-40 one last Async reference in GAE driver.
JCLOUDS-40 one last Async reference in Atmos.
JCLOUDS-152 remove RestContext and its dependencies.