In general, when we build a package, we want no compiler warnings
and all unit tests to pass.

That is in particular true when building a package for the distribution
in koji. When builing in koji, we (rightly) cannot pass rpmbuild options, so
the default whether tests/compiler-warnings are fatal matter very much.

One could argue: let's have the tests/compiler-warnings fatal and fail the build.
During a build in koji for a Fedora release, we want them all pass. And if somebody
does a manual build, the person can patch the spec file (or use rpmbuild
flags).

However, note how commit "f7b5e48c contrib/rpm: don't force fatal warnings
with tests" already disabled fatal compiler warnings. Why? It seems
compiler warnings should be even more stable than our unit tests, as long
as you target a particular Fedora release and compiler version. So this
was done to support rebuilding an SRPM for a different Fedora release,
or to be more graceful during early development phase of a Fedora
release, where things are not as stable yet.

The exactly same reasoning applies to treating unit-tests failures as fatal.
For example, a recent iproute2 issue broke unit tests. That meant, with
that iproute2 release in build root, the NetworkManager RPM could not be built.
Very annoying.

Now:

- if "test" is enabled, that means both `make check` and compiler warnings
  are treated fatal. If "test" is disabled, `make check` and compiler
  warnings are still done, just not fatal.

- "test" is now disabled by default via the spec file. They are not fatal
  when building in koji or when rebuilding the package manually.

- tests can be enabled optionally. Note that the "build_clean.sh"
  script enables them by default. So, a user using this script would
  need to explicitly "--without test".

(cherry picked from commit ad850c4f)