Disable this test on RHEL/CentOS 6

GnuTLS on RHEL 6 has minimal TLS 1.2 implementation and most of the
ciphersuites/features used in this test don't work there.

Author: mrc0mmand

gnutls/Interoperability/renegotiation-with-NSS/Makefile

@@ -59,5 +59,5 @@ $(METADATA): Makefile
 	@echo "License:         GPLv2" >> $(METADATA)
 	@echo "Confidential:    no" >> $(METADATA)
 	@echo "Destructive:     no" >> $(METADATA)
-	@echo "Releases:        -RHEL4 -RHELClient5 -RHELServer5" >> $(METADATA)
+	@echo "Releases:        -RHEL4 -RHELClient5 -RHELServer5 -RHEL6" >> $(METADATA)