Restarting the agent as non root shouldn't hang/go wacko

[cory-stripe]

Restarting the agent as an unprivileged user — i forgot sudo all the time — blindly tries to run even though it clearly can't make any changes! Maybe add a check at the beginning and bail out?

Additional environment details (Operating System, Cloud provider, etc):

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 14.04.5 LTS
Release:	14.04
Codename:	trusty

Steps to reproduce the issue:
Run /etc/init.d/datadog-agent restart as an unprivileged user.

Describe the results you received:

$ /etc/init.d/datadog-agent restart
 * Stopping Datadog Agent (stopping supervisord) datadog-agent
start-stop-daemon: warning: failed to kill 19164: Operation not permitted

Ended up ctrl-Z and kill -9ing the thing.

Describe the results you expected:
An error that I'm unprivileged and this won't work. :)

Additional information you deem important (e.g. issue happens only occasionally):
This is minor, but a nice ergonomic feature since it's really frustrating when you're trying to get something done.