Fix base docker images

Seems like quay.io/app-sre is no longer available to public and builds
fail. This commit fixes that by using registry.centos.org to get
centos:8 container image and our own quay.io/kuryr to host the
golang:1.15 image.

Change-Id: I044092e83b1a525ffd7692971a2e3313dfa1e421

cni.Dockerfile

@@ -1,10 +1,10 @@
-FROM quay.io/app-sre/golang:1.15 as builder
+FROM quay.io/kuryr/golang:1.15 as builder
 
 WORKDIR /go/src/opendev.com/kuryr-kubernetes
 COPY . .
 RUN go build -o /go/bin/kuryr-cni ./kuryr_cni
 
-FROM quay.io/app-sre/centos:8
+FROM registry.centos.org/centos:8
 LABEL authors="Antoni Segura Puimedon<toni@kuryr.org>, Michał Dulko<mdulko@redhat.com>"
 
 ARG UPPER_CONSTRAINTS_FILE="https://releases.openstack.org/constraints/upper/master"

controller.Dockerfile

@@ -1,4 +1,4 @@
-FROM quay.io/app-sre/centos:8
+FROM registry.centos.org/centos:8
 LABEL authors="Antoni Segura Puimedon<toni@kuryr.org>, Michał Dulko<mdulko@redhat.com>"
 
 ARG UPPER_CONSTRAINTS_FILE="https://releases.openstack.org/constraints/upper/master"