Add Single vs Multi server Install options

[vpiserchia]

As of now the current Role design only allows multi servers installation.

It would be nice to handle also the single server installation and described in the main documentation here: Single server Installation

This Issues has been created as an anwer to this #5

[sgc-ai]

#5

Related to this, if you attempt a single server install, the existing ansible role uses {{ proxy_port }} for the proxy as well as the agent, and will fail in its current default configuration.