* fixed bug in etcd retention where backups are not sorted by date

* added directory filter to find command

* added an ansible var to manage retention of etcd backups

* refactord ls/grep into find in etcd backup removal command

* Update etcd deployment to use correct cert and key

* Update to use admin cert for etcdctl commands

* Update handler to use admin cert too

* 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

Make etcd_backup_prefix configurable. Ensures that backups can be stored on a different location other than ${HOST}/var/backups, say an EBS volume on AWS.

- Run docker run from script rather than directly from systemd target
- Refactoring styling/templates

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

etcd is crucial part of kubernetes cluster. Ansible restarts etcd on
reconfiguration. Backup helps operator to restore cluster manually in
case of any issues.

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