image trigger should support `--wait`

[matthewmcnew]

https://github.com/pivotal/build-service-cli/issues/4 added support for --wait on image patches and creates. This allows users to follow the result of an kp action without executing build logs <image-name> and allows it to be used naturally in a ci automation context.

However, without --wait support on a trigger a user will not be able to use the same technique with an image trigger.