compat: add layer caching compatiblity for non podman clients

Non-podman clients do not set `layers` while making request. This is
supposed to be `true` bydefault but `non-podman-clients i.e Docker` dont
know about this field as a result they end up setting this values to
`false`. Causing builds to never use cache for layers.

Adds compatiblity for `docker SDK`.

[NO NEW TESTS NEEDED]

Signed-off-by: Aditya Rajan <arajan@redhat.com>

pkg/api/handlers/compat/images_build.go

@@ -134,6 +134,15 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// if layers field not set assume its not from a valid podman-client
+	// could be a docker client, set `layers=true` since that is the default
+	// expected behviour
+	if !utils.IsLibpodRequest(r) {
+		if _, found := r.URL.Query()["layers"]; !found {
+			query.Layers = true
+		}
+	}
+
 	// convert addcaps formats
 	var addCaps = []string{}
 	if _, found := r.URL.Query()["addcaps"]; found {