release_tarball: use make-dist if available

release_tarball: use make-dist if available

this enables us to prepare release tarball for versions without
autotools support, where we use make-dist to create the release tarball
instead.

- make-dist only produces .bz2 tarball, so we switch to .bz2 in this
  change.
- it's a waste to create both .gz and .bz2 tarballs using "make dist*",
  as we only use one of the to repackage the .gz and .bz2 tarballs.
  so let's drop "make dist" and use "make dist-bzip2" only.

Signed-off-by: Kefu Chai <kchai@redhat.com>