(MODULES-4604) move name validation in mysql_grant type

[eputnam]

Users are running into an issue where `puppet resource mysql_grant` fails because there is a global name validation using properties that only exist in a compiled catalog and not in the naked type that is instantiated during a `puppet resource` run. self[:user] and self[:table] are nil in this use case so there is a failure. This commit surrounds the validation in an if statement so it is not called during `puppet resource`. Also, a happy path test is added and the acceptance test is removed."

[LichP]

This validation still erroneously fails if user is passed in as an uninterpolated variable. For example:

$user_host = 'someuser@somehost'
$db_name = 'somedb'
mysql_grant { "${user_host}/${db_name}.*":
  ensure     => present,
  privileges => $tables_or_all,
  table      => "${db_name}.*",
  user       => $user_host,
}

The above snippet fails the validation check on 5.2.0 unless the user line is changed to user => "${user_host}",