Build on CentOS 6

[aanand]

Hopefully a solution to #102.

To check:

$ git clone https://github.com/aanand/fig.git
$ cd fig
$ git checkout build-on-centos6
$ script/build-linux
$ docker run -v `pwd`/dist/fig:/usr/bin/fig -i -t centos:centos6 fig --version

And if CentOS 6 is your host OS:

$ fig --version

[dduportal]

Hi, thanks for this PR : it works for centos:centos6 docker image but also for debian;7.6 !

Since i want to run fig inside a container with entry point to be portable, i' m playing around the lightweight possible image. I'll let you informed of busy box and other players as it.

[dduportal]

Some tests under different OSes (see trusted build tags) : https://registry.hub.docker.com/u/dduportal/fig/

[nathanleclaire]

I can confirm that fig provided with the curl option doesn't work due to the GLIB_C issue on Debian Wheezy (just installed it on a new server), but this PR fixes it!

[bfirsh]

This is a hack just to make pyinstaller work... maybe we should make a separate Dockerfile for building binaries? The root Dockerfile can then just be for running it.

[bfirsh]

If #454 does indeed work on Centos 6, I think I'd prefer using Debian.

[bfirsh]

Replaced by #505.