Commit logspout binary to repository; update Dockerfile reference and Makefile

Updated Makefile:
 - to have a stage/logspout target which copies the build output to the stage directory
 - to depend upon the stage/logspout when building the container
 - to force the OS/ARCH to be linux/amd64 (prevent Mac users from destroying the world)

Updated Dockerfile:
 - ADDs from the stage location