Builder fails to cleanup object store slugs

Destroying an app via Deis cli does not clean up the build slugs when app name fails to match regex.

Builder Version: 2.7.1
Storage Driver: Swift
Steps to reproduce:
`deis destroy --app=my-app`
`kubectl logs BUILDER --namespace=deis`

Only log line written is clearing the cache:
`Cleaner deleting cache home/my-app/cache for app my-app`

Missing the lines in code at #445

`log.Info("Cleaner deleting slug %s for app %s", obj, app)`

`my-app` had over 100 builds.

Issue is potentially the regex matching:

`gitRegex, err := regexp.Compile(`^/` + fmt.Sprintf(gitreceive.GitKeyPattern, app, ".{8}") + "$")`