Move docker version introspection to a sub-package.

This facilitates the refactoring of commands.go.

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

dockerversion/dockerversion.go

@@ -0,0 +1,11 @@
+package dockerversion
+
+// FIXME: this should be embedded in the docker/docker.go,
+// but we can't because distro policy requires us to
+// package a separate dockerinit binary, and that binary needs
+// to know its version too.
+
+var (
+	GITCOMMIT string
+	VERSION   string
+)