feat(builder): add repo check script

This script parses through /deis/services and removes all
repositories that have been removed from the controller.
feat(controller): set app dir in etcd

If you add or remove the app from the controller, the corresponding etcd
key is not modified. This ensures that the etcd keyspace is created/removed
when an app is modified in the database.
fix(controller): create /deis/services on boot

Some components such as the builder script in #1168 relies on
/deis/services to be present before booting.
test(builder): add /deis/services endpoint
fix(controller): use etcd_safe_mkdir
fix(controller): create directory only on create

If a modification is made to the app, then the underlying signal should
not tell etcd to re-create the directory or else etcd will complain that
you are trying to write to an already-existing directory.
docs(managing_deis): builder needs /deis/services
Merge pull request #1168 from deis/499-git-repo

fix(builder): delete the git repo on `apps:destroy`