Improve spec file and show details about failing tests in output.
- Fix License tag.
- Package COPYING.txt and use it with license macro.
(see libdfp-license.patch and upstream pull-request
https://github.com/libdfp/libdfp/pull/86)
- Remove Group and BuildRoot tags.
- Use buildroot macro instead of RPM_BUILD_ROOT variable.
- Do not remove buildroot during install step.
- Use pushd/popd instead of cd commands.
- Remove clean section.
- Fix changelog in order to not include macros.
- Print summary of failing tests in the output of make check.
(see libdfp-tests.patch and upstream pull-request
https://github.com/libdfp/libdfp/pull/87)
Signed-off-by: Stefan Liebler <stli@linux.ibm.com>