Add new nscd element

Provide an element that installs the nscd caching daemon.

Change-Id: Ib35d50388c7c82c6a527115fecc084969166a8fd
Add bandersnatch element

Add an element to create a bandersnatch pypi mirror. We can then
use this element to create ci mirrors local to each CI rack.

Change-Id: Ie29b38823c63cf320ecce42300c78b5e7ac80a59
Merge "Add new nscd element"
Merge "Add bandersnatch element"