package/wayland: don't build tests

package/wayland: don't build tests

wayland is entirely written in C, except for a single test that is
written in C++.

Since we are not interested in running the tests on the target, add an
option to configure to disable tests altogether.

Fixes:
    http://autobuild.buildroot.org/results/291/291e0f1ea18004190ae5acd9bec147cacc3e4bda/

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>