Change chef install method

[leonardofl]

Installing Chef with apt-get can sometimes lead to errors such as

$sudo apt-get update
...
W: Failed to fetch http://apt.opscode.com/dists/trusty-0.10/main/binary-i386/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

I believe now (after some experiences) that a better and simpler way to install Chef is using gem install, such as in:
https://github.com/radar-parlamentar/implantacao/blob/master/install_chef.sh

Obs: current way to install Chef is defined on:
https://github.com/choreos/enactment_engine/blob/master/EnactmentEngine/src/main/resources/chef-solo/bootstrap.sh