workunit: include ceph bin dir in path
workunit: include ceph bin dir in path

Some workunits need these binaries (e.g. kclient/file_layout.sh needs
cephfs).

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@newdream.net>

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