suite.py: tell you that the suite you asked for doesn't exist
suite.py: tell you that the suite you asked for doesn't exist

I know it's not in fashion to issue useful error messages, but...

Signed-off-by: Dan Mick <b07550071eaa6a9296289c43bbd6c90559196431@redhat.com>

SUSE/teuthology,SUSE/teuthology,ktdreyer/teuthology,ceph/teuthology,dmick/teuthology,ceph/teuthology,SUSE/teuthology,dmick/teuthology,dmick/teuthology,ktdreyer/teuthology