Add ssh-agent support

[cgty]

This change makes possible to use ssh-agent with a simple server option.

Instead of providing a password or pem file, one can simply pass "useAgent": true in pm2-meteor.json. By setting this value to true, SSH_AUTH_SOCK environment variable (which holds the unix-domain socket created by ssh-agent) will be passed to nodemiral.

This change will make possible to use encrypted private keys with pm2-meteor.

Fixes #36, #10

[xlinbsd]

Hello,
I confirm this feature is needed here, since I'm forced to reconfigure sshd of my hosts and lose ssh-agent advantages to be able to deploy.
Regards
[edit]
the above commit posted works

[vale981]

Bump