##### 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 global variables (instance settings)."""
        res = self.__exec_sql('SHOW GLOBAL VARIABLES')
        if res:
            for var in res:
                self.info['settings'][var['Variable_name']] = self.__convert(var['Value'])
            ver = self.info['settings']['version'].split('.')
            release = ver[2].split('-')[0]
            self.info['version'] = dict(
                major=int(ver[0]),
                minor=int(ver[1]),
                release=int(release),
            )
    def __get_global_status(self):
        """Get global status."""
        res = self.__exec_sql('SHOW GLOBAL STATUS')
        if res:
            for var in res:
                self.info['global_status'][var['Variable_name']] = self.__convert(var['Value'])
    def __get_master_status(self):
        """Get master status if the instance is a master."""
        res = self.__exec_sql('SHOW MASTER STATUS')
        if res:
            for line in res:
                for vname, val in iteritems(line):
                    self.info['master_status'][vname] = self.__convert(val)
    def __get_slave_status(self):