Properly pin ceph

Ubuntu is a bit different than centos. We aren't pinning a single ceph
verion because we cannot. We can however pin to a particular repo,
but we were not due to formating. This fixes that formating and pins
to a specific repo.

TrivialFix

Change-Id: I2f6c4cd2f7d51652dc2729c0ab384165151e94e2

docker/base/apt_preferences

 Package: *
-Pin: origin "download.ceph.com", v=0.94.5-1trusty
+Pin: origin download.ceph.com
 Pin-Priority: 700
 
 Package: mesos
 Pin: version 0.27.1
-Pin-Priority: 700
\ No newline at end of file
+Pin-Priority: 700