##### 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

RETURN = r'''
version:
  description: Database server version.
  returned: if not excluded by filter
  type: dict
  sample: { "version": { "major": 5, "minor": 5, "release": 60 } }
  contains:
    major:
      description: Major server version.
      returned: if not excluded by filter
      type: int
      sample: 5
    minor:
      description: Minor server version.
      returned: if not excluded by filter
      type: int
      sample: 5
    release:
      description: Release server version.
      returned: if not excluded by filter
      type: int
      sample: 60
databases:
  description: Information about databases.
  returned: if not excluded by filter
  type: dict
  sample:
  - { "mysql": { "size": 656594 }, "information_schema": { "size": 73728 } }
  contains:
    size: