test/openssl/test_ssl: skip test_fallback_scsv if necessary

[ This is a backport to the 2.1 branch. ]

Run the test case only when the OpenSSL supports both TLS 1.1 and TLS
1.2. Note that the fallback SCSV mechanism is for TLS 1.2 or older and
not for 1.3.

Fixes: #336
(cherry picked from commit 6f2e6d7)

Author: rhenium

test/test_ssl.rb

@@ -1377,6 +1377,10 @@ def test_get_ephemeral_key
   end
 
   def test_fallback_scsv
+    supported = check_supported_protocol_versions
+    return unless supported.include?(OpenSSL::SSL::TLS1_1_VERSION) &&
+      supported.include?(OpenSSL::SSL::TLS1_2_VERSION)
+
     pend "Fallback SCSV is not supported" unless \
       OpenSSL::SSL::SSLContext.method_defined?(:enable_fallback_scsv)