Add tests for the padding extension

Check that the padding extension pads correctly for various scenarios.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2968)
diff --git a/test/recipes/70-test_clienthello.t b/test/recipes/70-test_clienthello.t
index ef0868f..ccb3a5a 100644
--- a/test/recipes/70-test_clienthello.t
+++ b/test/recipes/70-test_clienthello.t
@@ -7,7 +7,7 @@
 # https://www.openssl.org/source/license.html
 
 
-use OpenSSL::Test;
+use OpenSSL::Test qw/:DEFAULT srctop_file/;
 use OpenSSL::Test::Utils;
 
 setup("test_clienthello");
@@ -17,4 +17,5 @@
 
 plan tests => 1;
 
-ok(run(test(["clienthellotest"])), "running clienthellotest");
+ok(run(test(["clienthellotest", srctop_file("test", "session.pem")])),
+   "running clienthellotest");