NCBC-583: Ensure Dispose is call on every MD5CryptoServiceProvider class usage

Change-Id: Iae83cd67765c74c9d50d3e982b9f750d61804816
Reviewed-on: http://review.couchbase.org/41121
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Brett Lawson <brett19@gmail.com>