This adds the ability to build CentOS packages from Fedora - scylla
already has it. Aside from that, this guarantees that the build will
work in any system. In particular, by default rpmbuild is not given
network access in some of the systems I tested, causing the build to
fail as it tries to contact the maven repo.
This file is just a copy of the one provided by Centos' mock, with
the option to allow rpmbuild network added.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
