Makefile: Add simple dev loop

Add a `dev` target which adds a convenient developer loop which
rebuilds and reruns the daemon after a SIGINT is received.

It can be exited by sending SIGINT (Ctrl+C) a couple times.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

hack/dev.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+while true; do
+	if ! ./hack/make.sh binary; then
+		# If the build fails, sleep for 5 seconds and continue
+		sleep 5
+		continue
+	fi
+	KEEPBUNDLE=1 ./hack/make.sh install-binary || continue
+
+	dockerd --debug || true
+	sleep 0.1
+done