Use system variable for ECR repository

ECR repositories are stored in system variables. Use this
so that CI can work parellly to the one in upstream.

Change-Id: Id75bb5a49305a7abc059741f8bcb4e60595fbf1a
Signed-off-by: Saheer Babu <saheer.babu@arm.com>
diff --git a/fvp-docker-images/builders.sh b/fvp-docker-images/builders.sh
index 3cbb4b8..27d1581 100644
--- a/fvp-docker-images/builders.sh
+++ b/fvp-docker-images/builders.sh
@@ -17,9 +17,9 @@
 git log -1
 
 aws configure list
-ECR=987685672616.dkr.ecr.us-east-1.amazonaws.com
+export ECR=${PRIVATE_CONTAINER_REGISTRY}
 aws s3 cp --recursive s3://openci-trustedfirmware-fvp-${INFRA_ENV}/ .
-aws ecr get-login-password --region us-east-1|docker login --username AWS --password-stdin $ECR
+aws ecr get-login-password --region eu-west-1|docker login --username AWS --password-stdin $ECR
 
 
 for tarball in F*.tgz