* Create a standard element to copy manifests out of the image and
into the build area.
* Ensure all current manifests are copied into a standard manifests
directory
Change-Id: I37eff5a13a14564e1adc33eb4f0144d571267617
Cloning large repositories over the internet can take considerable
time. Caching them locally makes repeated image builds significantly
faster, so lets do that.
When users override the element source they will often be using a
local repository, so in those cases I don't cache - but we could
easily change our minds on that in the future.
Change-Id: I9822362cf722b904d9806dbbb4bb07cfe2b33437