bundle install in the build, so we don't use bundle in the tests
exclude server gems for chef-10 builds
adding docgen
set Omnibus cache build path for `pip install` commands

By default pip uses "<OS temp dir>/pip-build-<username>", which can 
cause failures on long-lived build slaves.
do a bundle install before gem install, otherwise the gem
  install may install versions of gems that do not match the
  bundle and we want to preserve exactly the bundle contents
fix paths to use the omnibus stuff that we've installed
missing libgcc dep
require modern gmake instead of removing parallellism
prefer gmake for openssl
reference to removed build_jobs variable