Pulsar: use cluster-base as base image
Pulsar: use cluster-base as base image

So we can share the same base as the Galaxy
server itself (see earlier commits).
This is also in preparation for connecting
Pulsar with HTCondor and Slurm, and to
run containers using Pulsar.

chambm/docker-galaxy-stable,chambm/docker-galaxy-stable,chambm/docker-galaxy-stable,bgruening/docker-galaxy-stable,bgruening/docker-galaxy-stable,bgruening/docker-galaxy-stable