##### 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 storage engines info."""
        res = self.__exec_sql('SHOW ENGINES')
        if res:
            for line in res:
                engine = line['Engine']
                self.info['engines'][engine] = {}
                for vname, val in iteritems(line):
                    if vname != 'Engine':
                        self.info['engines'][engine][vname] = val
    def __convert(self, val):
        """Convert unserializable data."""
        try:
            if isinstance(val, Decimal):
                val = float(val)
            else:
                val = int(val)
        except ValueError:
            pass
        except TypeError:
            pass
        return val
    def __get_global_variables(self):