fix(cleaner): remove the usage of watch api

[kmala]

Summary of Changes

remove the usage of watch api and instead get the namespaces to know which apps are deleted because the watch api is flaky and also the channel gets closed too often kubernetes/kubernetes#8700

Issue(s) that this PR Closes

closes #287

Associated End To End Test PR(s)

deis/workflow-e2e#182

Associated Documentation PR(s)

Associated Design Document(s)

Testing Instructions

Please provide a detailed list for how to test the changes in this PR.

1. Create a Deis Cluster
2. deploy an app using git push
3. check in the builder pod and the app should be present in the /home/git/ folder
4. delete the app
5. again check the builder pod and now it should not be present in the /home/git/ folder

Pull Request Hygiene TODOs

Please make sure the below checklist is complete.

• Your pull request is concise and to the point (make another PR for refactoring nearby code)
• Your commits are squashed into logical units of work
• Your commits follow the commit style guidelines

[arschles]

Historical note: the original implementation of the cleaner used a similar polling approach but suffered from some concurrency issues. See #186 for the initial implementation and #209 for the changes to using the watch API. Added for context

[arschles]

@kmala code LGTM (although needs rebase). does this need manual testing?

also, not blocking for this PR, but can you create an issue in deis/workflow-e2e to add an end-to-end test to test the cleaner (iirc there isn't one, but if you know of one, then ignore)