This patch removes code which detected http proxies being set in
environment variables, and inserted an apt configuration instructing
those proxies not to perform caching.
This lack of caching reduces the effectiveness of an http proxy which
has caching enabled - a common technique for increasing performance of
operating system installs without having to run a full mirror of
upstream repositories.
If a deployer is faced with a proxy server which in some way breaks
upstream package repository interactions, this no-cache setting can be
applied by the deployer as part of host preparation and will be
duplicated into containers by the OSA tooling.
Change-Id: I62293c723353ffb986db1cddc5d0da20ae0df447
3c3f4c09d8