tests: conditionalize output in test-ssh.t with chg+py3
Because of our wrapping around sys.std* and python3 internal buffering, the
output order changes. The change in order seems like harmless because just few
lines above the same command is run which results in same output.
This makes test-ssh.t works with --chg on python 3.
Differential Revision: https://phab.mercurial-scm.org/D9502