Provide support for multiple $PORT values per process

[padcom]

Use-case:

Starting services with separate administration interface, for example ActiveMQ or MongoDB

Current state:

There's no way to start applications that require more than one port to function properly.

Expected state:

Can declare for example $PORT1 and $PORT2 and those will properly be populated taking into account the amount of declared ports when running multiple processes of the same kind. Possibly it'd make sense to change the port number increment between processes from 100 to 100xnumber of ports

[ddollar]

This is a level of complexity I'd rather not add to foreman

[ClayShentrup]

How does process 2 know how to access process 1?