Add regression tests for lua support

Change Dockerfile to install lua, luajit and love and also to install
nodejs 12 needed to build the lua debug adapter. Create the
love-headless test in support/test/lua to test love without an x server.

support/test/lua/love-headless/conf.lua

@@ -0,0 +1,12 @@
+function love.conf(t)
+    t.modules.audio = false
+    t.modules.font = false
+    t.modules.graphics = false
+    t.modules.image = false
+    t.modules.mouse = false
+    t.modules.physics = false
+    t.modules.sound = false
+    t.modules.touch = false
+    t.modules.video = false
+    t.modules.window = false
+end