Remove the hard dependency on CAP_SYS_ADMIN (partial fix for #167)

[thomasdesr]

Changes made

Implements the solution (new environment variable) discussed in #167. I left the default as the old behavior to avoid breaking anything.

In the Dockerfile I switched patch into whitespace-insensitive mode because getting the whitespace byte-for-byte equivalent was taking longer than the rest of the changes combined.

Testing

Seems to be up and running happily on my setup :D

I explicitly tested the docker run command and everything seems to come up happily. Unfortunately I don't have a good way to test the docker-compose changes but I think they're right :S

[fryfrog]

Neat! I'll give this a try in my instance and see how it does. :)

[fryfrog]

I just restarted my container w/ the new arguments and image, came up just fine. We'll see how it goes, then I can put it on release. :)