Bugfix: GenerateClusterISO failing in subsystem tests
The latest coreos-installer:release version was compiled with a newer
glibc version (2.32). Switching to an older tag.
-FROM quay.io/coreos/coreos-installer:release AS installer-image
+FROM quay.io/coreos/coreos-installer:v0.7.0 AS installer-image
# Build binaries
FROM registry.svc.ci.openshift.org/openshift/release:golang-1.14 as builder
