Updated openstack/openstack
Project: openstack-dev/devstack  fa5282e89c911f486889a6b0bfeaf6a111312798

Increase CEPH_LOOPBACK_DISK_SIZE_DEFAULT to 4GB

CEPH_LOOPBACK_DISK_SIZE_DEFAULT should be more than 2GB
to make volume snapshot feature works. 2GB is not enough
because min Cinder volume size is 1GB and no snapshot
could be created.

This also fixes related Tempest tests and experimental
check-tempest-dsvm-full-ceph gate job.

Change-Id: Ifa41d0d1764d68ea02dcb32a5fc62f7f6282904d