ref(builder): remove volume definition in Dockerfile

This was missed in #1917.
fix(builder): exec the runner
fix(builder): Non-root slugrunner and slugbuilder

This improves the compatibility to heroku and stops running apps as root
fix(builder): Reverted to default php buildpack

The pervious compatibility fixes made the heroku php build pack work
out-of-the-box again
Merge pull request #1984 from carmstrong/remove_builder_volume

ref(builder): remove volume definition in Dockerfile
fix(builder): restore VOLUME instruction so builder does not stack overlay filesystems

fix(builder): add comment explaining dockerfile volume change
Merge pull request #1996 from gabrtv/fix-builder-volume

fix(builder): restore VOLUME instruction so builder does not stack overlay filesystems
ref(tests): update details in CI node setup script
Merge pull request #1983 from mboersma/test-setup-tweaks

ref(tests): update details in CI node setup script
fix(controller): Use correct entrypoint for run

Running commands in an image build using git push requires to use
‘/runner/init’ as entrypoint, otherwise environment variables inject by
buildpacks are missing.

Fixes #1801, fixes #1568
Merge pull request #1972 from johanneswuerbach/buildpack-env

fix(builder): Non-root slugrunner and slugbuilder
docs(installing_deis): remove xip.io instructions for ELB

xip.io simply doesn't work for ELBs - it returns an IP of
54.64.0.0 which obviously isn't a valid IP.

I suspect it works for CNAMEs in general, but not for CNAMEs
which resolve to multiple IPs, as ELBs do.
Merge pull request #1985 from johanneswuerbach/run-env

fix(controller): Use correct entrypoint for run
Merge pull request #2003 from carmstrong/remove_xip_io

docs(installing_deis): remove xip.io instructions for ELB
feat(tests): Show all etcd keys on error

This should help debugging all those `ERROR Config check failed: exit status 1` errors.
Merge pull request #2009 from johanneswuerbach/patch-6

feat(tests): Show all etcd keys on error