patch 8.0.0805: GUI test fails with gnome2

Problem:    GUI test fails with gnome2.
Solution:   Set $HOME to an existing directory.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 0256d48..c57ec5f 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -158,6 +158,9 @@
   " Don't write viminfo on exit.
   set viminfo=
 
+  " Clean up files created by setup.vim
+  call delete('XfakeHOME', 'rf')
+
   if s:fail == 0
     " Success, create the .res file so that make knows it's done.
     exe 'split ' . fnamemodify(g:testname, ':r') . '.res'