By default enabled but one can disable it by passing --disable-xwayland-test
to the configure script. Also, the weston-tests-env script is trying to load
xwayland.so in either case, but it behaves resilient in the absence of that
meaning all the other tests are still going to be kicked for running.

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>