misc: make get_scratch_devices look for (almost) any disk that's not mounted
misc: make get_scratch_devices look for (almost) any disk that's not mounted

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