tests/docker: Update the Fedora image to Fedora 30

Fedora 30 got released:

  https://fedoramagazine.org/announcing-fedora-30/Signed-off-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: NStefano Garzarella <sgarzare@redhat.com>
Reviewed-by: NStefano Garzarella <sgarzare@redhat.com>
Message-Id: <20190528153304.27157-1-philmd@redhat.com>
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>

tests/docker/dockerfiles/fedora.docker

-FROM fedora:29
+FROM fedora:30
 ENV PACKAGES \
     bc \
     bison \