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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 -->

SELECT COLUMN_NAME FROM information_schema.COLUMNS
                WHERE TABLE_SCHEMA = 'mysql' AND TABLE_NAME = 'user' AND COLUMN_NAME IN ('Password', 'authentication_string')
                ORDER BY COLUMN_NAME DESC LIMIT 1
            """)
            colA = cursor.fetchone()
            cursor.execute("""
                SELECT COLUMN_NAME FROM information_schema.COLUMNS
                WHERE TABLE_SCHEMA = 'mysql' AND TABLE_NAME = 'user' AND COLUMN_NAME IN ('Password', 'authentication_string')
                ORDER BY COLUMN_NAME ASC  LIMIT 1
            """)
            colB = cursor.fetchone()
            
            cursor.execute("""
                SELECT COALESCE(
                        CASE WHEN %s = '' THEN NULL ELSE %s END,
                        CASE WHEN %s = '' THEN NULL ELSE %s END
                    )
                FROM mysql.user WHERE user = %%s AND host = %%s
                """ % (colA[0], colA[0], colB[0], colB[0]), (user, host))
            current_pass_hash = cursor.fetchone()[0]
            if isinstance(current_pass_hash, bytes):
                current_pass_hash = current_pass_hash.decode('ascii')
            if encrypted:
                encrypted_password = password
                if not is_hash(encrypted_password):
                    module.fail_json(msg="encrypted was specified however it does not appear to be a valid hash expecting: *SHA1(SHA1(your_password))")
            else:
                if old_user_mgmt:
                    cursor.execute("SELECT PASSWORD(%s)", (password,))
                else: