travis: Enforcing SREE_VERSION
travis: Enforcing SREE_VERSION

As per issue #1076, detecting the latest SREE_VERSION fails in Travis.
This patch simply try to enforce a default version as a workaround.

Fixes: #1076

Signed-off-by: Erwan Velu <dbf153a4f846e5c13692f4d75719ee25e7660abd@redhat.com>

ceph/ceph-docker,ceph/ceph-docker