Use the configured username for _make_scratch_dir
Use the configured username for _make_scratch_dir

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