Makefile: Adding push.parallel target
Makefile: Adding push.parallel target

When the CI runs, it have to build images and then push them to the registry.

This push target takes some time and slow down the whole build process.

This patch is about adding parallelism on this process. It reuse the
same principles used in build.parallel target

Signed-off-by: Erwan Velu <dbf153a4f846e5c13692f4d75719ee25e7660abd@redhat.com>

JrCs/ceph-docker,JrCs/ceph-docker,ceph/ceph-docker,ceph/ceph-docker,JrCs/ceph-docker