Empty /etc files installed / packaged

[dtrudg]

Type of issue

packaging

Description of issue

In the review for the addition of singularity-ce to Fedora (https://bugzilla.redhat.com/show_bug.cgi?id=2145834) it was noted that RPMLint finds we install some zero length files:

> RPMLint:
> 
> > singularity-ce.x86_64: E: zero-length /etc/singularity/capability.json
> > singularity-ce.x86_64: E: zero-length /etc/singularity/global-pgp-public

For now an rpmlintrc rule was added, but we should verify whether these files can be safely created at runtime, as it is definitely odd to package zero length files if not absolutely necessary.