Make running under supervisord (eg. Docker) possible about pdagent

[divtxt]

@analytically - can you give me some idea of where/how you'll be using each of these options?

Security practices recommend against running as root which is why we currently prevent it

[azretd]

I would like to second this request.

For one, Docker does not allow applications to use init.d or upstart, thus most applications have to use a process like supervisord or runit to loop the foreground process. Having a foreground option in pdagent would allow us to use services such as these to run the application.

Secondly, root isn't necessary. We can run applications as other users.

[mlewis033]

#100 provides the -f option to run in foreground now