fix(tests): Allow TLS

Fixes https://github.com/deis/deis/issues/2230
docs(installing_deis): import gce provisioning docs
ref(installing_deis): remove unused link
chore(release): update version in master to v0.15.1+git
docs(managing_deis): add MDS removal instructions
docs(*): specify required CoreOS version
Merge pull request #2367 from mboersma/release-0.15.1+git

chore(release): update version in master to v0.15.1+git
Merge pull request #2352 from johanneswuerbach/patch-6

fix(tests): Allow TLS
fix(build.sh): fail on errors in Dockerfile two-tier builds

Without "set -e" at the top of each build.sh script, errors would
not propagate to the parent "docker build" process. In the case
of controller, this was masking a missing dependency which is now
fixed.
fix(registry): prefix "apt-get install" with "apt-get update"
Merge pull request #2368 from carmstrong/docs-add_remove_mds

docs(managing_deis): add MDS removal instructions
Merge pull request #2369 from carmstrong/add_coreos_version

docs(*): specify required CoreOS version
Merge pull request #2362 from mboersma/catch-build-sh-errors

fix(build.sh): fail on errors in Dockerfile two-tier builds
Merge pull request #2365 from bacongobbler/gce-docs-import

docs(installing_deis): import gce provisioning docs
fix(deisctl/units): mount deis-store only if it isn't mounted
Merge pull request #2379 from carmstrong/pr-2363

fix(deisctl/units): mount deis-store only if it isn't mounted