test-serve: use service that works on more platforms

Follow-up to ba8850911703: echo is ambiguous on OS/X, and Solaris have neither
http nor gopher. daytime seems to be available everywhere.

tests/test-serve

@@ -40,9 +40,9 b' hgserve'
 echo % With -v and -p HGPORT2
 hgserve -p "$HGPORT2"
 
-echo '% With -v and -p echo (should fail because low port)'
+echo '% With -v and -p daytime (should fail because low port)'
 KILLQUIETLY=Y
-hgserve -p echo
+hgserve -p daytime
 KILLQUIETLY=N
 
 echo % With --prefix foo

tests/test-serve.out

@@ -7,8 +7,8 b' listening at http://localhost/ (bound to'
 % With -v and -p HGPORT2
 listening at http://localhost/ (bound to 127.0.0.1:HGPORT2)
 % errors
-% With -v and -p echo (should fail because low port)
-abort: cannot start server at 'localhost:7': Permission denied
+% With -v and -p daytime (should fail because low port)
+abort: cannot start server at 'localhost:13': Permission denied
 abort: child process failed to start
 % errors
 % With --prefix foo