tests: load the right xwayland plugin

If we do not specify the full path to xwayland.so, Weston can find an
old one installed in a $prefix and use that instead of the freshly built
one.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/tests/weston-tests-env b/tests/weston-tests-env
index 746ae27..fb9928a 100755
--- a/tests/weston-tests-env
+++ b/tests/weston-tests-env
@@ -22,13 +22,15 @@
 fi
 
 BACKEND=$abs_builddir/.libs/$BACKEND
+TEST_PLUGIN=$abs_builddir/.libs/weston-test.so
+XWAYLAND_PLUGIN=$abs_builddir/.libs/xwayland.so
 
 case $TESTNAME in
 	*.la|*.so)
 		$WESTON --backend=$BACKEND \
 			--no-config \
 			--socket=test-$(basename $TESTNAME) \
-			--modules=$abs_builddir/.libs/${TESTNAME/.la/.so},xwayland.so \
+			--modules=$abs_builddir/.libs/${TESTNAME/.la/.so},$XWAYLAND_PLUGIN \
 			--log="$SERVERLOG" \
 			&> "$OUTLOG"
 		;;
@@ -38,6 +40,6 @@
 			--backend=$BACKEND \
 			--no-config \
 			--log="$SERVERLOG" \
-			--modules=$abs_builddir/.libs/weston-test.so,xwayland.so \
+			--modules=$TEST_PLUGIN,$XWAYLAND_PLUGIN \
 			&> "$OUTLOG"
 esac