Standardise manifest creation and retrieval

Bring in line with the manifest standardisation in review
I37eff5a13a14564e1adc33eb4f0144d571267617

This:
    * Removes the pip-manifest cleanup script and corresponding
      README documentation
    * Adds a dependency on the manifests element
    * Uses the manifests element for manifest location and copy to
      build area
    * Standardises the manifest naming

Change-Id: I8ab0796a8e19419bf40c1ebc94a7eb04e3ba9180
Merge "Standardise manifest creation and retrieval"