run-tests: when running in parallel, delete tmpdirs immediately
This is especially important if extensions that use inotify are enabled,
because it's very easy to hit the inotify max_user_instances limit without
this.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state