test/test_engine: check if RC4 is supported

Skip test_openssl_engine_cipher_rc4 which will fail without RC4 support.
It may be disabled by 'no-rc4' configure option of the OpenSSL library.

Reference: #154

Author: rhenium

test/test_engine.rb

@@ -52,9 +52,15 @@ def test_openssl_engine_digest_sha1
   end
 
   def test_openssl_engine_cipher_rc4
+    begin
+      OpenSSL::Cipher.new("rc4")
+    rescue OpenSSL::Cipher::CipherError
+      pend "RC4 is not supported"
+    end
+
     with_openssl(<<-'end;', ignore_stderr: true)
       engine = get_engine
-      algo = "RC4" #AES is not supported by openssl Engine (<=1.0.0e)
+      algo = "RC4"
       data = "a" * 1000
       key = OpenSSL::Random.random_bytes(16)
       encrypted = crypt_data(data, key, :encrypt) { engine.cipher(algo) }