redhat/self-test: Ignore .rhpkg.mk files
If a user specifies, for example, a ~/.rhpkg.mk file, the file will be
included in the MAKEFILE_LIST variable. This breaks the
dist-dump-variables test, so these files should be excluded.
Ignore user specified .rhpkg.mk files.
Signed-off-by: Prarit Bhargava prarit@redhat.com