feat(controller): expose app url

While users should not have access to view a cluster's private
information like the cluster's auth key or the list of machines,
we need the cluster domain in order to expose the app url to the
user.
fix(builder): set /app as working directory for apps

When you run commands with Heroku, you are running under
/app as the intial directory.
test(controller): add unit tests for app-related permission checks
fix(controller): honor app permissions correctly on app-related views
chore(logger): update go to 1.3.1

Also updated to go 1.3.1 in our etcd test container.
Merge pull request #1599 from bacongobbler/builder-workdir

fix(builder): set /app as working directory for apps
Merge pull request #1582 from bacongobbler/903-apps-open

fix(controller): expose app URL
Merge pull request #1603 from mboersma/logger-golang-131

chore(logger): update go to 1.3.1
Merge pull request #1602 from mboersma/1576-fix-deis-ps-perms

fix(controller): honor permissions on app-related views