Elide creating Build when the Build portion of the Configuration doesn't change.

[mattmoor]

This TODO.

[mattmoor]

cc @imjasonh

[mattmoor]

Just found out that riff is currently relying on this, so we should be sensitive to not breaking them.

cc @trisberg

[trisberg]

If we could add the annotation to the build part instead of the revisionTemplate then that would work fine for our purposes

[mattmoor]

@trisberg With decoupled build in 0.2 you can start doing this.

Before:

build:
  <spec>

After:

build:
  apiVersion: build.knative.dev/v1alpha1
  kind: Build
  metadata:
    annotations:
      # Since we will treat the entire "build" as opaque, any change should
      # trigger a new build, so this would serve a similar purpose to the nonce
      # @seyfer has proposed for forcing redeployments via the CLI.
      whatever/you: want
  spec:
    <spec>