teuthology/run: use default value for better readability
teuthology/run: use default value for better readability

Signed-off-by: Kefu Chai <a4b264ee037c625052534d60505bfd0db4776ac4@redhat.com>

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