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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 -->

__metaclass__ = type
ANSIBLE_METADATA = {'metadata_version': '1.1',
                    'status': ['preview'],
                    'supported_by': 'community'}
DOCUMENTATION = r'''
---
module: mysql_user
short_description: Adds or removes a user from a MySQL database
description:
   - Adds or removes a user from a MySQL database.
version_added: "0.6"
options:
  name:
    description:
      - Name of the user (role) to add or remove.
    type: str
    required: true
  password:
    description:
      - Set the user's password..
    type: str
  encrypted:
    description:
      - Indicate that the 'password' field is a `mysql_native_password` hash.
    type: bool
    default: no
    version_added: "2.0"
  host:
    description:
      - The 'host' part of the MySQL username.