fix(contrib/userdata): nse uses `docker exec`

Fixes shells into the container not having the correct envvars
docs(deisctl): reword comment
Merge pull request #2348 from Xe/fix/contrib-user-data/nse-uses-docker-exec

fix(contrib/userdata): nse uses `docker exec`
docs(README.md): replace moved DNS link
docs(contrib): replace moved DNS links
Merge pull request #2358 from Paperback/patch-1

docs(README.md): replace moved DNS link
docs(installing_deis): import baremetal docs
docs(contrib): refer to digitalocean guide
docs(testing): add better instructions for contributors
ref(docs): error on warnings for all Makefile targets
docs(*): add Troubleshooting Deis docs
Merge pull request #2346 from ngpestelos/patch-1

docs(deisctl): reword comment
Merge pull request #2361 from bacongobbler/import-do-docs

docs(contrib): refer to digitalocean guide
Merge pull request #2360 from bacongobbler/baremetal-docs-import

docs(installing_deis): import baremetal docs
Merge pull request #2336 from mboersma/testing-docs

docs(testing): add better instructions for contributors
Merge pull request #2359 from carmstrong/docs-add_troubleshooting_deis

docs(*): add Troubleshooting Deis docs
chore(release): update version to v0.15.1
Merge pull request #2366 from mboersma/release-0.15.1

chore(release): update version to v0.15.1
chore(release): update version in master to v0.15.1+git
Merge pull request #2367 from mboersma/release-0.15.1+git

chore(release): update version in master to v0.15.1+git