Remove system buildpacks

Remove tests associated with system buildpacks
Merge branch 'removebuildpacks' of github.com:fraenkel/dea_ng

* Resolved some conflicts caused by changes from PR #114

Signed-off-by: Ruth Byers <rbyers@pivotallabs.com>

Conflicts:
	lib/dea/staging/buildpack_manager.rb
	lib/dea/staging/staging_task_workspace.rb
	spec/unit/staging/buildpack_manager_spec.rb
	spec/unit/staging/staging_task_workspace_spec.rb