patch 8.0.1179: Test_popup_and_window_resize() does not always pass

Problem:    Test_popup_and_window_resize() does not always pass.
Solution:   Do not use $VIMPROG, pass the Vim executable in the vimcmd file.
            (Ozaki Kiichi, closes #2186)
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index fdd51de..917395b 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -643,10 +643,10 @@
   if h < 15
     return
   endif
-  let g:buf = term_start([$VIMPROG, '--clean', '-c', 'set noswapfile'], {'term_rows': h / 3})
-  call term_sendkeys(g:buf, (h / 3 - 1)."o\<esc>G")
-  call term_sendkeys(g:buf, "i\<c-x>")
+  let g:buf = term_start([GetVimProg(), '--clean', '-c', 'set noswapfile'], {'term_rows': h / 3})
+  call term_sendkeys(g:buf, (h / 3 - 1)."o\<esc>")
   call term_wait(g:buf, 200)
+  call term_sendkeys(g:buf, "Gi\<c-x>")
   call term_sendkeys(g:buf, "\<c-v>")
   call term_wait(g:buf, 100)
   " popup first entry "!" must be at the top