##### SUMMARY

`mysql_info` module doesn't show empty DBs. It uses following query in the code:

```
MariaDB [(none)]> SELECT table_schema AS 'name', SUM(data_length + index_length) AS "size" FROM information_schema.TABLES GROUP BY table_schema;
+--------------------+-----------+
| name               | size      |
+--------------------+-----------+
| d106953_tm         | 470728704 |
| information_schema |    212992 |
| mysql              |   6038300 |
| performance_schema |         0 |
+--------------------+-----------+
4 rows in set (0,005 sec)
```
But `show databases` show something else;
```
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| d106953_tm         |
| information_schema |
| innodb             |
| mysql              |
| performance_schema |
| testovic           |
| tm_web             |
| ttttt              |
+--------------------+
8 rows in set (0,001 sec)
```

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
`mysql_info` modules

##### ANSIBLE VERSION
```
ansible 2.9.1
  config file = /home/jiri/.ansible.cfg
  configured module search path = ['/home/jiri/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/jiri/stow/ansible/venv/lib/python3.6/site-packages/ansible
  executable location = /home/jiri/stow/ansible/venv/bin/ansible
  python version = 3.6.9 (default, Nov  7 2019, 10:44:02) [GCC 8.3.0]

```

##### OS / ENVIRONMENT
Amazon Linux 2
rh-mariadb103-3.3-5.el7.x86_64

##### STEPS TO REPRODUCE

* create empty via eg. via `mysql_db module`
* query via `mysql_info` what databases where found

##### EXPECTED RESULTS
should list even empty DBs

##### ACTUAL RESULTS

it seems only populated DBs are listed
"""Class for collection MySQL instance information.
    Arguments:
        module (AnsibleModule): Object of AnsibleModule class.
        cursor (pymysql/mysql-python): Cursor class for interaction with
            the database.
    Note:
        If you need to add a new subset:
        1. add a new key with the same name to self.info attr in self.__init__()
        2. add a new private method to get the information
        3. add invocation of the new method to self.__collect()
        4. add info about the new subset to the DOCUMENTATION block
        5. add info about the new subset with an example to RETURN block
    """
    def __init__(self, module, cursor):
        self.module = module
        self.cursor = cursor
        self.info = {
            'version': {},
            'databases': {},
            'settings': {},
            'global_status': {},
            'engines': {},
            'users': {},
            'master_status': {},
            'slave_hosts': {},
            'slave_status': {},
        }
    def get_info(self, filter_, exclude_fields):