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/main.lua

@@ -0,0 +1,10 @@
+if pcall(require, 'lldebugger') then
+  require('lldebugger').start()
+end
+
+local time = 0
+
+function love.update(dt)
+  time = time + dt
+  love.event.quit()
+end