Refine RNG usage

- Create instance once, bind it to ShadowsocksController

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

test/UnitTest.cs

@@ -68,6 +68,7 @@ namespace test
 
         private void RunEncryptionRound(IEncryptor encryptor, IEncryptor decryptor)
         {
+            RNG.Reload();
             byte[] plain = new byte[16384];
             byte[] cipher = new byte[plain.Length + 16 + IVEncryptor.ONETIMEAUTH_BYTES + IVEncryptor.AUTH_BYTES];
             byte[] plain2 = new byte[plain.Length + 16];
@@ -117,6 +118,7 @@ namespace test
             {
                 t.Join();
             }
+            RNG.Close();
             Assert.IsFalse(encryptionFailed);
         }
 
@@ -156,6 +158,7 @@ namespace test
             {
                 t.Join();
             }
+            RNG.Close();
             Assert.IsFalse(encryptionFailed);
         }
 
@@ -196,6 +199,7 @@ namespace test
             {
                 t.Join();
             }
+            RNG.Close();
             Assert.IsFalse(encryptionFailed);
         }