Run brats pipeline jobs on all supported stacks
Run brats pipeline jobs on all supported stacks

- Add the r, nginx, and hwc buildapcks to the pipeline

[#160301603]

Co-authored-by: Daniel Thornton <5874b3971aa460e96f75d4dbef8f6aadb66f1697@pivotal.io>

cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci