tests: use progress helper
With this commit, the only in-tree caller of ui.progress() is
scmutil.progress(). That means that we could deprecate it. It also
means that we can considering inlining it in scmutil.progress.
Differential Revision: https://phab.mercurial-scm.org/D3812
cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh=python "$TESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF