feat(tests): add test-nightly.sh script for CI

To be used by our nightly buildpack / Dockerfile regression testing
jobs at http://ci.deis.io/view/example-apps/.
docs(contrib): update docs with deisctl
Merge pull request #1894 from mboersma/1893-nightly-tests

feat(tests): add test-nightly.sh script for CI
fix(tests): make test-nightly.sh executable
chore(router): Updated nginx to 1.6.2

This fixes a security issue in 1.6.1 http://nginx.org/
docs(releases): update release procedure with deisctl tasks
Merge pull request #1897 from bacongobbler/contrib-docs

docs(contrib): update docs with deisctl
Merge pull request #1899 from mboersma/update-release-checklist

docs(releases): update release procedure with deisctl tasks
Merge pull request #1898 from johanneswuerbach/patch-5

chore(router): Updated nginx to 1.6.2
docs(CHANGELOG): update for v0.12.0
chore(release): update version to v0.12.0