[docs] Update docs for slave installation

[Artur Kaszuba]

We have procedure for install jenkins slave server, page https://docs.fuel-infra.org/fuel-dev/ci/overview.html
This description is not actual, we don't use swarm. It also misses information about hiera configuration and possible options.

Please update description for slave installation:
- should contain requirements for base system, for example Ubuntu with ssh, dns on server which allow to resolve puppet domain, etc
- what is needed to configure on puppet master to install slave, what files should be created/changed, add examples
- what is needed to execute on slave and master to apply puppet manifests, with examples
- describe possible options which could be set in hiera and will be used by slave manifest
- describe how to connect jenkins slave to jenkins master

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/258451

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/258451
Committed: https://git.openstack.org/cgit/openstack/fuel-web/commit/?id=7c8c86af23c342f7b9ded1def083dc371029a91c
Submitter: Jenkins
Branch: master

commit 7c8c86af23c342f7b9ded1def083dc371029a91c
Author: Mateusz Matuszkowiak <email address hidden>
Date: Tue Dec 29 16:42:03 2015 +0100

    jenkins slave deployment doc related to Fuel infra

    Change-Id: Ied78f4eab6462e01c65a74109d525cf3aa7dcdb7
    Related-Bug: #1510535