support omnibus removal on all platforms

This mainly targets platforms where omnibus chef is installed with self-
extractable archives (makeself).
move linux build lab to a subfolder

This will allow the build lab to better support other non-linux
platforms.
[CHEF-2576] adjust post inst/rm scripts for SmartOS

SmartOS writes data to `/opt/local` so we should link data to
`/opt/local/bin` instead of `/usr/bin`.
[CHEF-2576] add SmartOS build lab
WIP Gemfile, Berksfile - REVERT BEFORE MERGE