The default package set installed on macOS builders from Travis already
includes libffi and gettext as shown by log messages:
Skipping install of libffi formula. It is already up-to-date.
Using libffi
Skipping install of gettext formula. It is already up-to-date.
Using gettext
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>