test-serve: make the 'listening at *' lines optional

The daemonized serve process doesn't print these lines out (see 448d0c452140).
I was able to get it to with the following hack:

 diff --git a/mercurial/win32.py b/mercurial/win32.py
 --- a/mercurial/win32.py
 +++ b/mercurial/win32.py
 @@ -418,6 +418,11 @@
          return str(ppid)

  def spawndetached(args):
 +
 +    import subprocess
 +    return subprocess.Popen(args, cwd=pycompat.getcwd(), env=encoding.environ,
 +                            creationflags=subprocess.CREATE_NEW_PROCESS_GROUP).pid
 +
      # No standard library function really spawns a fully detached
      # process under win32 because they allocate pipes or other objects
      # to handle standard streams communications. Passing these objects

However, MSYS translates --prefixes starting with '/' to 'C:/MinGW/msys/1.0',
which changes the output.  The output isn't so important that I want to spend a
bunch of time on this, and risk breaking some subtle behavior of `hg serve -d`
with the more complicated code.

tests/test-hgwebdir.t

@@ -1421,7 +1421,7 b' test listening address/port specified by'
   > EOF
   $ hg serve -d --pid-file=hg.pid --web-conf paths.conf \
   >     -A access-paths.log -E error-paths-9.log
-  listening at http://*:$HGPORT1/ (bound to *$LOCALIP*:$HGPORT1) (glob)
+  listening at http://*:$HGPORT1/ (bound to *$LOCALIP*:$HGPORT1) (glob) (?)
   $ cat hg.pid >> $DAEMON_PIDS
   $ get-with-headers.py localhost:$HGPORT1 '?style=raw'
   200 Script output follows
@@ -1433,7 +1433,7 b' test --port option overrides web.port:'
   $ killdaemons.py
   $ hg serve -p $HGPORT2 -d -v --pid-file=hg.pid --web-conf paths.conf \
   >     -A access-paths.log -E error-paths-10.log
-  listening at http://*:$HGPORT2/ (bound to *$LOCALIP*:$HGPORT2) (glob)
+  listening at http://*:$HGPORT2/ (bound to *$LOCALIP*:$HGPORT2) (glob) (?)
   $ cat hg.pid >> $DAEMON_PIDS
   $ get-with-headers.py localhost:$HGPORT2 '?style=raw'
   200 Script output follows

tests/test-patchbomb-tls.t

@@ -7,7 +7,7 b' Set up SMTP server:'
 
   $ python "$TESTDIR/dummysmtpd.py" -p $HGPORT --pid-file a.pid -d \
   > --tls smtps --certificate `pwd`/server.pem
-  listening at localhost:$HGPORT
+  listening at localhost:$HGPORT (?)
   $ cat a.pid >> $DAEMON_PIDS
 
 Set up repository:

tests/test-serve.t

@@ -34,13 +34,13 b' errors'
 With -v
 
   $ hgserve
-  listening at http://localhost/ (bound to *$LOCALIP*:HGPORT1) (glob)
+  listening at http://localhost/ (bound to *$LOCALIP*:HGPORT1) (glob) (?)
   % errors
 
 With -v and -p HGPORT2
 
   $ hgserve -p "$HGPORT2"
-  listening at http://localhost/ (bound to *$LOCALIP*:HGPORT2) (glob)
+  listening at http://localhost/ (bound to *$LOCALIP*:HGPORT2) (glob) (?)
   % errors
 
 With -v and -p daytime (should fail because low port)
@@ -57,25 +57,25 b' With -v and -p daytime (should fail beca'
 With --prefix foo
 
   $ hgserve --prefix foo
-  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob)
+  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob) (?)
   % errors
 
 With --prefix /foo
 
   $ hgserve --prefix /foo
-  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob)
+  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob) (?)
   % errors
 
 With --prefix foo/
 
   $ hgserve --prefix foo/
-  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob)
+  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob) (?)
   % errors
 
 With --prefix /foo/
 
   $ hgserve --prefix /foo/
-  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob)
+  listening at http://localhost/foo/ (bound to *$LOCALIP*:HGPORT1) (glob) (?)
   % errors
 
   $ cd ..