tests: remove sleep/startup/shutdown races from test-hup

tests/test-hup.t

@@ -5,16 +5,22 b' Test hangup signal in the middle of tran'
   $ mkfifo p
   $ hg serve --stdio < p &
   $ P=$!
-  $ (echo lock; echo addchangegroup; sleep 5) > p &
-  $ Q=$!
-  $ sleep 3
+
+Do test while holding fifo open
+
+  $ (
+  > echo lock
+  > echo addchangegroup
+  > while [ ! -e .hg/store/00changelog.i.a ]; do true; done
+  > kill -HUP $P
+  > while kill -0 $P 2>/dev/null; do true; done
+  > ) > p
   0
   0
   adding changesets
-  $ kill -HUP $P
-  $ wait
   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