default to deleting images via the remote api

This makes the remote API version 1.12 and newer default to
automatically deleting intermediate containers when the build has
succeedeed.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)

api/client/commands.go

@@ -198,6 +198,8 @@ func (cli *DockerCli) CmdBuild(args ...string) error {
 	}
 	if *rm {
 		v.Set("rm", "1")
+	} else {
+		v.Set("rm", "0")
 	}
 
 	if *forceRm {

api/server/server.go

@@ -903,8 +903,11 @@ func postBuild(eng *engine.Engine, version version.Version, w http.ResponseWrite
 	} else {
 		job.Stdout.Add(utils.NewWriteFlusher(w))
 	}
+
 	if r.FormValue("forcerm") == "1" && version.GreaterThanOrEqualTo("1.12") {
 		job.Setenv("rm", "1")
+	} else if r.FormValue("rm") == "" && version.GreaterThanOrEqualTo("1.12") {
+		job.Setenv("rm", "1")
 	} else {
 		job.Setenv("rm", r.FormValue("rm"))
 	}

docs/sources/reference/api/docker_remote_api_v1.12.md

@@ -1063,7 +1063,7 @@ Build an image from Dockerfile via stdin
         the resulting image in case of success
     -   **q** – suppress verbose build output
     -   **nocache** – do not use the cache when building the image
-    -   **rm** - remove intermediate containers after a successful build
+    -   **rm** - remove intermediate containers after a successful build (default behavior)
     -   **forcerm - always remove intermediate containers (includes rm)
 
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