Use an upstream riemann release

[jmcarp]

Our riemann release is forked from https://github.com/hybris/riemann-boshrelease with some cherry-picked commits from https://github.com/xoebus/riemann-boshrelease and has significantly diverged from both. Since both upstream releases both allow injecting arbitrary riemann config files via job properties, we shouldn't need an independent fork. We also have a few semi-related jobs like riemann-checklogs and riemann-checkawslogs in our release, but as @cnelson pointed out, those probably belong in a separate release.

Tasks:

• Choose an upstream riemann release
• Factor related jobs into a separate release

cc @sharms