tests: make test-hup more race-proof

We need to wait until a journal exists AND is non-empty before
aborting a transaction to get stable output. We move the kill wait
outside the fifo block to avoid potential deadlock.

tests/test-hup.t

@@ -1,26 +1,28 b''
 Test hangup signal in the middle of transaction
 
   $ "$TESTDIR/hghave" serve fifo || exit 80
   $ hg init
   $ mkfifo p
-  $ hg serve --stdio < p &
+  $ hg serve --stdio < p 1>out 2>&1 &
   $ P=$!
 
 Do test while holding fifo open
 
   $ (
   > echo lock
   > echo addchangegroup
-  > while [ ! -e .hg/store/00changelog.i.a ]; do true; done
+  > while [ ! -s .hg/store/journal ]; do true; done
   > kill -HUP $P
-  > while kill -0 $P 2>/dev/null; do true; done
   > ) > p
+
+  $ while kill -0 $P 2>/dev/null; do true; done
+  $ cat out
   0
   0
   adding changesets
   transaction abort!
   rollback completed
   killed!
 
   $ echo .hg/* .hg/store/*
   .hg/00changelog.i .hg/journal.bookmarks .hg/journal.branch .hg/journal.desc .hg/journal.dirstate .hg/requires .hg/store .hg/store/00changelog.i .hg/store/00changelog.i.a .hg/store/journal.phaseroots