patch 8.0.1697: various tests are still a bit flaky

Problem:    Various tests are still a bit flaky.
Solution:   Increase the default wait time to five seconds.
diff --git a/src/testdir/test_clientserver.vim b/src/testdir/test_clientserver.vim
index 6ef6428..b807ecc 100644
--- a/src/testdir/test_clientserver.vim
+++ b/src/testdir/test_clientserver.vim
@@ -32,7 +32,7 @@
 
   " Takes a short while for the server to be active.
   " When using valgrind it takes much longer.
-  call WaitFor('serverlist() =~ "' . name . '"', 5000)
+  call WaitFor('serverlist() =~ "' . name . '"')
   call assert_match(name, serverlist())
 
   call remote_foreground(name)