Update Dockerfile for dashboard deployment
Update Dockerfile for dashboard deployment

Fixing a couple of issues that can cause failures in the creation of
docker image dashboard-base:
* ENV PATH is moved earlier since its value is needed by the
  /usr/local/depot_tools/vpython command.
* Add --allow-releaseinfo-change switch to apt-get command, since the
  image contains an older version of Linux.

Bug: chromium:1241577
Change-Id: I3eaea318acdf7ac25f019658d223d0153a6a0066
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/3582555
Reviewed-by: Sean McCullough <7caa448b00260c603c5227306703b63f5f75ff01@google.com>
Reviewed-by: Leina Sun <4dc7485e04f6a3a1d05495d5781efc53aef710e0@google.com>
Commit-Queue: John Chen <334fbfbb4df7c78f091ea1b77c69ca6ac731a3f3@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult