added a test for teuthology.orchestra.cluster.write_file
added a test for teuthology.orchestra.cluster.write_file

Signed-off-by: Andrew Schoen <1bb641dc23c3a93cce4eee683bcf4b2bea7903a3@redhat.com>

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