Fix unit-test-docker proxy handling
Fix unit-test-docker proxy handling

This change introduces setting correct proxy setting for keyserver
resolution during docker build.

Testing:
- docker successfully builds and runs image behind corporate proxy

Change-Id: I15a2d09cc62f7405cc14a8e41c7863fee01548be
Signed-off-by: Adrian Ambrożewicz <5d596128d78c438d49333a98311ba7a5bf287c3e@intel.com>

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts