##### 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

description: Database size in bytes.
      returned: if not excluded by filter
      type: dict
      sample: { 'size': 656594 }
settings:
  description: Global settings (variables) information.
  returned: if not excluded by filter
  type: dict
  sample:
  - { "innodb_open_files": 300, innodb_page_size": 16384 }
global_status:
  description: Global status information.
  returned: if not excluded by filter
  type: dict
  sample:
  - { "Innodb_buffer_pool_read_requests": 123, "Innodb_buffer_pool_reads": 32 }
  version_added: "2.10"
users:
  description: Users information.
  returned: if not excluded by filter
  type: dict
  sample:
  - { "localhost": { "root": { "Alter_priv": "Y", "Alter_routine_priv": "Y" } } }
engines:
  description: Information about the server's storage engines.
  returned: if not excluded by filter
  type: dict
  sample:
  - { "CSV": { "Comment": "CSV storage engine", "Savepoints": "NO", "Support": "YES", "Transactions": "NO", "XA": "NO" } }
master_status: