remove ohai dev gems

the sigar gem makes solaris and freebsd very unhappy
add comment about possible cargo cult
we use static libgcc now
fixup ohai to remove dev gems

removes the bundle exec from 'rake gem', also should handle the
appbuilder case for chefdk correctly.
Merge pull request #237 from opscode/lcg/remove-ohai-dev-gems

remove ohai dev gems