##### SUMMARY
mysql_user module with check_implicit_admin=yes try to connect to database without password. But when login failed doesn't fallback to login_user and login_password credentials.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
mysql_user

##### ANSIBLE VERSION
```
2.9.0
```

##### OS / ENVIRONMENT
Ubuntu 18.04

##### STEPS TO REPRODUCE
```yaml
- name: Update root password for all root accounts
  mysql_user: name=root password={{ mysql_root_password }} login_user=root login_password={{ mysql_root_password }} host={{ item }} check_implicit_admin=yes
  with_items:
    - "{{ current_hostname.stdout | lower }}"
    - 127.0.0.1
    - ::1
    - localhost
```

First run is ok, but on second run Ansible failed when try to connect as root without password and no fallback to login credentials.

##### EXPECTED RESULTS
First run -> root / no password
Other runs -> root / mysql_root_password

##### ACTUAL RESULTS
Provision failed at other as first run

"""Get MySQL instance information based on filter_.
        Arguments:
            filter_ (list): List of collected subsets (e.g., databases, users, etc.),
                when it is empty, return all available information.
        """
        self.__collect(exclude_fields)
        inc_list = []
        exc_list = []
        if filter_:
            partial_info = {}
            for fi in filter_:
                if fi.lstrip('!') not in self.info:
                    self.module.warn('filter element: %s is not allowable, ignored' % fi)
                    continue
                if fi[0] == '!':
                    exc_list.append(fi.lstrip('!'))
                else:
                    inc_list.append(fi)
            if inc_list:
                for i in self.info:
                    if i in inc_list:
                        partial_info[i] = self.info[i]
            else:
                for i in self.info:
                    if i not in exc_list:
                        partial_info[i] = self.info[i]
            return partial_info
        else:
            return self.info
    def __collect(self, exclude_fields):