Add new "DOCKER_CLIENTONLY" build variable to allow skipping of the dockerinit compilation, especially for Homebrew / Mac OS X client-only compilation

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

hack/PACKAGERS.md

@@ -181,6 +181,12 @@ the file "./VERSION". This binary is usually installed somewhere like
 
 ### Dynamic Daemon / Client-only Binary
 
+If you are only interested in a Docker client binary, set `DOCKER_CLIENTONLY` to a non-empty value using something similar to the following: (which will prevent the extra step of compiling dockerinit)
+
+```bash
+export DOCKER_CLIENTONLY=1
+```
+
 If you need to (due to distro policy, distro library availability, or for other
 reasons) create a dynamically compiled daemon binary, or if you are only
 interested in creating a client binary for Docker, use something similar to the

hack/make/dynbinary

@@ -2,6 +2,7 @@
 
 DEST=$1
 
+if [ -z "$DOCKER_CLIENTONLY" ]; then
 	# dockerinit still needs to be a static binary, even if docker is dynamic
 	go build \
 		-o $DEST/dockerinit-$VERSION \
@@ -28,6 +29,10 @@ fi
 	
 	# sha1 our new dockerinit to ensure separate docker and dockerinit always run in a perfect pair compiled for one another
 	export DOCKER_INITSHA1="$($sha1sum $DEST/dockerinit-$VERSION | cut -d' ' -f1)"
+else
+	# DOCKER_CLIENTONLY must be truthy, so we don't need to bother with dockerinit :)
+	export DOCKER_INITSHA1=""
+fi
 # exported so that "dyntest" can easily access it later without recalculating it
 
 (