Add condition at adding password to post body
Update get_body_3 to have application credential body if auth type is
 set to v3applicationcredentail

Add three variables:
 app_cred_id, app_cred_secret, and openstack_auth_type
Define validate_auth_type method
Move password, username required check into validate_auth_type method
 since application credential doesnt require username and password
Update validate_api_version method
 since application credential doesnt require other variables like:
 user_domain or project_name

app_cred_id_required and app_cred_secret_required

Add app_cred_id and app_cred_secret
Add keystone_request_body_app_cred
Add context with good application credentials
Add context with wrong application credentials