openisr-config: Clean up DKMS code
openisr-config: Clean up DKMS code

- Use Perl rather than grep pipelines to determine the DKMS status

- Minor cleanups to build_redhat()

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr