A few changes for singularity (BMK-77)

@chollowe your MR succeeded, thanks :-)

I am adding a few more changes for singularity here. Then I will add others (I have two other open braches where I touched related things).

Here I am just moving to the kaniko CI, and changing a few names.

build-executor/singularity/Dockerfile

@@ -11,11 +11,7 @@ LABEL multi.maintainer="Chris Hollowell <hollowec@bnl.gov>" \
 
 RUN yum clean all
 
-RUN yum install -y singularity-runtime
+RUN yum install -y singularity-runtime && yum clean all
+
 RUN sed -i -e 's/underlay = no/underlay = yes/g' /etc/singularity/singularity.conf
 RUN sed -i -e 's/overlay = try/overlay = no/g' /etc/singularity/singularity.conf
-
-ARG CACHEBUST=1
-
-RUN echo CACHEBUST=$CACHEBUST
-