Add cram task
Add cram task

This runs cram tests, which are an easy way to test output
stays consistent. We already use cram for basic cli tests with no cluster,
and now we can use it for whole system tests too.

SUSE/teuthology,dmick/teuthology,michaelsevilla/teuthology,ceph/teuthology,robbat2/teuthology,dmick/teuthology,yghannam/teuthology,caibo2014/teuthology,SUSE/teuthology,ivotron/teuthology,tchaikov/teuthology,caibo2014/teuthology,SUSE/teuthology,zhouyuan/teuthology,michaelsevilla/teuthology,ktdreyer/teuthology,t-miyamae/teuthology,dreamhost/teuthology,dmick/teuthology,ceph/teuthology,t-miyamae/teuthology,robbat2/teuthology,zhouyuan/teuthology,dreamhost/teuthology,ktdreyer/teuthology,ivotron/teuthology,yghannam/teuthology,tchaikov/teuthology