<!--- Verify first that your feature was not already discussed on GitHub -->
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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 -->

# user=root
# password=n<_665{vS43y
'''
import re
import string
from ansible.module_utils.basic import AnsibleModule
from ansible.module_utils.database import SQLParseError
from ansible.module_utils.mysql import mysql_connect, mysql_driver, mysql_driver_fail_msg
from ansible.module_utils.six import iteritems
from ansible.module_utils._text import to_native
VALID_PRIVS = frozenset(('CREATE', 'DROP', 'GRANT', 'GRANT OPTION',
                         'LOCK TABLES', 'REFERENCES', 'EVENT', 'ALTER',
                         'DELETE', 'INDEX', 'INSERT', 'SELECT', 'UPDATE',
                         'CREATE TEMPORARY TABLES', 'TRIGGER', 'CREATE VIEW',
                         'SHOW VIEW', 'ALTER ROUTINE', 'CREATE ROUTINE',
                         'EXECUTE', 'FILE', 'CREATE TABLESPACE', 'CREATE USER',
                         'PROCESS', 'PROXY', 'RELOAD', 'REPLICATION CLIENT',
                         'REPLICATION SLAVE', 'SHOW DATABASES', 'SHUTDOWN',
                         'SUPER', 'ALL', 'ALL PRIVILEGES', 'USAGE', 'REQUIRESSL',
                         'CREATE ROLE', 'DROP ROLE', 'APPLICATION PASSWORD ADMIN',
                         'AUDIT ADMIN', 'BACKUP ADMIN', 'BINLOG ADMIN',
                         'BINLOG ENCRYPTION ADMIN', 'CONNECTION ADMIN',
                         'ENCRYPTION KEY ADMIN', 'FIREWALL ADMIN', 'FIREWALL USER',
                         'GROUP REPLICATION ADMIN', 'PERSIST RO VARIABLES ADMIN',
                         'REPLICATION SLAVE ADMIN', 'RESOURCE GROUP ADMIN',
                         'RESOURCE GROUP USER', 'ROLE ADMIN', 'SET USER ID',
                         'SESSION VARIABLES ADMIN', 'SYSTEM VARIABLES ADMIN',
                         'VERSION TOKEN ADMIN', 'XA RECOVER ADMIN',
                         'LOAD FROM S3', 'SELECT INTO S3'))
class InvalidPrivsError(Exception):