make sure we don't hard code the path for py.test
make sure we don't hard code the path for py.test

Signed-off-by: Alfredo Deza <3ae498813ac9b6992b3bb72690656738fc9b4e19@inktank.com>

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