make aws default docker registry in remaining scripts

AWS has much better anonymous pull request limits (1 per second) vs
docker hub which is 100 per 6 hours per IP address. A lot of our CI and
development occurs on shared systems so it's easy to exceed this limit
on an IP basis.

Tested:
- Verified no setting for DOCKER_REG and a setting of docker.io work as
  expected within these scripts

Change-Id: Ic5cb5ee07ee83567b6cf26754b6d1045025bdd65
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/qemu-build.sh b/qemu-build.sh
index 54044e7..5baa02e 100755
--- a/qemu-build.sh
+++ b/qemu-build.sh
@@ -22,8 +22,8 @@
 #  WORKSPACE          Path of the workspace directory where the build will
 #                     occur, and output artifacts will be produced.
 #  DOCKER_REG:        <optional, the URL of a docker registry to utilize
-#                     instead of the default docker hub
-#                     (ex. public.ecr.aws/ubuntu)
+#                     instead of our default (public.ecr.aws/ubuntu)
+#                     (ex. docker.io)
 #
 ###############################################################################
 # Trace bash processing
@@ -37,7 +37,7 @@
     exit 1
 fi
 
-docker_reg=${DOCKER_REG:-"docker.io"}
+docker_reg=${DOCKER_REG:-"public.ecr.aws/ubuntu"}
 
 # Docker Image Build Variables:
 img_name=qemu-build