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##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
New Percona/MySQL 8 privileges with underscore is not working. 
the following error is coming 

`MSG: invalid privileges string: Invalid privileges specified: frozenset({'BACKUP_ADMIN'})`

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
mysql_user module
most likely the new privileges needs to be added to lib/ansible/modules/database/mysql/mysql_user.py

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

<!--- HINT: You can also paste gist.github.com links for larger files -->

""" MySQL doesn't have a better method of getting privileges aside from the
    SHOW GRANTS query syntax, which requires us to then parse the returned string.
    Here's an example of the string that is returned from MySQL:
     GRANT USAGE ON *.* TO 'user'@'localhost' IDENTIFIED BY 'pass';
    This function makes the query and returns a dictionary containing the results.
    The dictionary format is the same as that returned by privileges_unpack() below.
    """
    output = {}
    cursor.execute("SHOW GRANTS FOR %s@%s", (user, host))
    grants = cursor.fetchall()
    def pick(x):
        if x == 'ALL PRIVILEGES':
            return 'ALL'
        else:
            return x
    for grant in grants:
        res = re.match("""GRANT (.+) ON (.+) TO (['`"]).*\\3@(['`"]).*\\4( IDENTIFIED BY PASSWORD (['`"]).+\\6)? ?(.*)""", grant[0])
        if res is None:
            raise InvalidPrivsError('unable to parse the MySQL grant string: %s' % grant[0])
        privileges = res.group(1).split(", ")
        privileges = [pick(x) for x in privileges]
        if "WITH GRANT OPTION" in res.group(7):
            privileges.append('GRANT')
        if "REQUIRE SSL" in res.group(7):
            privileges.append('REQUIRESSL')
        db = res.group(2)
        output[db] = privileges
    return output
def privileges_unpack(priv, mode):