Add ansible.cfg file

* set the default hosts file
* disable retry files by default
* always show the diff

Also edited README to remove -i
6 jobs for add_ansible_cfg in 39 seconds (queued for 1 second)
Status Job ID Name Coverage
  Galaxy
passed galaxy:install #4623
preprod

00:00:32

 
  Test Syntax
passed syntax:check #4626
preprod

00:00:03

failed syntax:check #4624
preprod

00:00:02

 
  Test Ansible
failed ansible:check #4657
preprod

00:00:03

failed ansible:check #4627
preprod

00:00:02

failed ansible:check #4625
preprod

00:00:03

 
Name Stage Failure
failed
ansible:check Test Ansible
PLAY [all] *********************************************************************

TASK [Gathering Facts] *********************************************************
fatal: [pi3.lqdn.fr]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Host key verification failed.\r\n", "unreachable": true}

PLAY RECAP *********************************************************************
pi3.lqdn.fr : ok=0 changed=0 unreachable=1 failed=0

ERROR: Job failed: exit status 1