mysql_user module: adding support for various REQUIRE options

This is a cleaned up version of #8750.

This PR introduces 5 new parameters into the module:
- require_ssl
- require_x509
- require_subject
- require_issuer
- require_cipher

More information about their purpose can be found [here](http://dev.mysql.com/doc/refman/5.1/en/grant.html).