Rename from aggregator-proxy-client to front-proxy-client to match kubeadm design. Added kubeadm support too. Changed to use variables set and not hardcode paths. Still missing cert generation for Vault

import_tasks will consume far less memory, so it should be
used whenever it is compatible.

* Cleaning up cert checks for vault

* Removing all unnecessary etcd certs from each node

* Removing all unnecessary kube certs from each node

  * using separated vault roles for generate certs with different `O` (Organization) subject field;
  * configure vault roles for issuing certificates with different `CN` (Common name) subject field;
  * set `CN` and `O` to `kubernetes` and `etcd` certificates;
  * vault/defaults vars definition was simplified;
  * vault dirs variables defined in kubernetes-defaults foles for using
  shared tasks in etcd and kubernetes/secrets roles;
  * upgrade vault to 0.8.1;
  * generate random vault user password for each role by default;
  * fix `serial` file name for vault certs;
  * move vault auth request to issue_cert tasks;
  * enable `RBAC` in vault CI;

* Added custom ips to etcd vault distributed certificates

* Added custom ips to kube-master vault distributed certificates

* Added comment about issue_cert_copy_ca var in vault/issue_cert role file

* Generate kube-proxy, controller-manager and scheduler certificates by vault

* Revert "Disable vault from CI (#1546)"

This reverts commit 781f31d2.

* Fixed upgrade cluster with vault cert manager

* Remove vault dir in reset playbook

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

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