tests/test-mq-qsave.t

testlib: add a small scrip to help process to synchronise using file

Creating and waiting for files is a robust way to synchronise two processes
running concurrently. We already use this approach in various tests. I am adding
a official script to do so before adding more usage of this.

Differential Revision: https://phab.mercurial-scm.org/D8189

  $ 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