[eduVPN-deploy] deploy script changes

[François Kooman]

Hi,

I made a couple of changes to the deploy script to easy installation on
some virtual machines and to accommodate deploys where Let's Encrypt is
not available or not wanted.

The internal API (between the components) now uses the "localhost"
virtual host as to not require a trusted SSL certificate for
communication between the components. This was required to work around
some issues on VMs where "floating IPs" were used.

The need to integrate Let's Encrypt in the deploy was thus no longer
there, so we're back to self signed certificates on initial deploy. Some
deploys do not want to use Let's Encrypt or are unable to because of CAA
records in DNS that indicate which certificate issuers can be used.
Getting a Let's Encrypt certificate installed is easy with the provided
script.

These changes make it also possible again to easily deploy the VPN
server on e.g. a VM running on your machine or any other machine where
no public IP or proper DNS name is available.

The documentation also changed as bit, CentOS has now a separate
document describing the steps to follow, including Let's Encrypt and
(experimentally) switching to PHP 7.1.

See [1] for the CentOS instructions, which is also linked from the main
page [2].

If you already deployed a server, you do not need to take any action,
things will keep working as-is!

Let me know if you have any questions!

Cheers,
François

[1] https://github.com/eduvpn/documentation/blob/master/DEPLOY_CENTOS.md
[2] https://github.com/eduvpn/documentation