Cleaned up packaging
    
    This basically contains the same clean-up as done in master, f26 and f25.
    
    - Lots of cleaning up in %configure and %install sections, including
      removing no longer valid and correcting errornous ./configure options
    - Use %systemd_* macros
    - Update the deprecated openvpn@.service unit file to work better
      with OpenVPN v2.4
    - Added README.systemd describing the new unit files
    - Cleaned up %files section, reduce files this package owns
    - Don't mix %doc and %{_pkgdocdir} - also avoids duplicated files in RPMs
    - Splitting out -devel files into a separate package
    - Removed several contrib and sample files which makes is not
      strictly needed in this package.
    - build: Enable tests runs by default, long running tests can
      be disabled with "--without tests_long"
    - build: Removed defined %%{plugins} macro not in use
    - Added .rpmlint to whitelist false positives
    
    Resolves: rhbz#1435831, rhbz#1435036, rhbz#850257
    Backport based on commit 6cb5c83b665431804700e197244103e98c164c62 and
    commit ba1a3a70779d6521d856bb33fc2ce5945cd3e144.