* Adding yaml linter to ci check

* Minor linting fixes from yamllint

* Changing CI to install python pkgs from requirements.txt

- adding in a secondary requirements.txt for tests
- moving yamllint to tests requirements

to match this https://github.com/kubernetes-incubator/kubespray/blob/master/roles/kubernetes/node/tasks/main.yml#L20
and the documented behaviour in HA docs 
related to #1456
@rsmitty

- Fix when clauses in various places
- Update requirements.txt
- Fix README.md

Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

When VPC is used, external DNS might not be available. This patch change
behavior to use metadata service instead of external DNS when
upstream_dns_servers is not specified.

Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

kubernetesUnitPrefix was changed to k8s_* in 1.5. This patch reflects
this change in kargo

Until now it was not possible to add an API Loadbalancer
without an static IP Address. But certain Loadbalancers
like AWS Elastic Loadbalanacer dontt have an fixed IP address.
With this commit it is possible to add these kind of Loadbalancers
to the Kargo deployment.

Updates based on feedback

Simplify checks for file exists

remove invalid char

Review feedback. Use regular systemd file.

Add template for docker systemd atomic

* Leave all.yml to keep only optional vars
* Store groups' specific vars by existing group names
* Fix optional vars casted as mandatory (add default())
* Fix missing defaults for an optional IP var
* Relink group_vars for terraform to reflect changes

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

Sometimes, a sysadmin might outright delete the SELinux rpms and
delete the configuration. This causes the selinux module to fail
with
```
IOError: [Errno 2] No such file or directory: '/etc/selinux/config'\n",
"module_stdout": "", "msg": "MODULE FAILURE"}
```

This simply checks that /etc/selinux/config exists before we try
to set it Permissive.

Update from feedback

Migrate older inline= syntax to pure yml syntax for module args as to be consistant with most of the rest of the tasks
Cleanup some spacing in various files
Rename some files named yaml to yml for consistancy

"shell" step doesn't support check mode, which currently leads to failures,
when Ansible is being run in check mode (because Ansible doesn't run command,
assuming that command might have effect, and no "rc" or "output" is registered).

Setting "check_mode: no" allows to run those "shell" commands in check mode
(which is safe, because those shell commands doesn't have side effects).

restart the controller to get the new file configuration.
I'm not fond of this form and would like a better way, but this
seems to "work".

always_run was deprecated in Ansible 2.2 and will be removed in 2.4
ansible logs contain "[DEPRECATION WARNING]: always_run is deprecated.
Use check_mode = no instead". This patch fix deprecation.

if the system doesn't have any config files at all.