remove bzip2 config

Upstream now maintains an omnibus-software config for bzip2 that we
can use instead.
update dependencies

Switch Gemfile to use the github shortcut for both omnibus and
omnibus-software gems.
Ugh!  Deal with omnibus API churn

For some reason, max_build_jobs was renamed to workers in ff7d627e7
without explanation.  Update gmp & sqlite3 omnibus-software configs
to cope.  :(
update to Ansible v1.7.2

Update to latest Ansible release.  While here, replace install_path
with install_dir because (again) upstream broke API backwards
compatibility without explanation (commit a0b503d).  :(