packaging: Update go install instructions for Debian wheezy

Docker requires go 1.1 to build, but Debian wheezy 'golang' is go 1.0.
Update the instructions to instead get the 1.1 binary distribution,
just like the build box from the Vagrantfile does.

Also get rid of the golang build dependency, as that conflicts with
the manually installed go binary.

This should fix issue #2

Signed-off-by: Kai Blin <kai@samba.org>