Makefile: add NODE custom variable support
Makefile: add NODE custom variable support

Makes it easy to plug in a different node executable to test with.

hoozi/co,luxe-eng/valet-express.co,Jonekee/co,f0rmat1k/co,abbshr/co,tj/co,pjeby/co3-devsuite,seegno-forks/co,guangfu/co,TakayukiSakai/co,cgvarela/co,VasylHryha/co,gyson/co,gradecam/co