patch 8.0.0479: remote_peek() is not tested

Problem:    remote_peek() is not tested.
Solution:   Add a test.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 832d97e..b896443 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -247,6 +247,8 @@
   call RunTheTest(s:test)
 
   if len(v:errors) > 0 && index(s:flaky, s:test) >= 0
+    call add(s:messages, 'Found errors in ' . s:test . ':')
+    call extend(s:messages, v:errors)
     call add(s:messages, 'Flaky test failed, running it again')
     let v:errors = []
     call RunTheTest(s:test)