patch 8.1.1483: skipped tests are not properly listed

Problem:    Skipped tests are not properly listed.
Solution:   Throw a "Skipped" exception instead of using ":finish" or ":return".
diff --git a/src/testdir/test_clientserver.vim b/src/testdir/test_clientserver.vim
index 5c01ac4..3377f86 100644
--- a/src/testdir/test_clientserver.vim
+++ b/src/testdir/test_clientserver.vim
@@ -1,7 +1,7 @@
 " Tests for the +clientserver feature.
 
 if !has('job') || !has('clientserver')
-  finish
+  throw 'Skipped: job and/or clientserver feature missing'
 endif
 
 source shared.vim