Pr expcliv2 (Koenkk#1344)

* Add multiplatform support

Using the experimental manifest support in docker one can
create a manifest that contain references to other images/tags
build for various architectures. When someone pulls koenkk/zigbee2mqtt
correct image is automatically selected.

Please note that experimental cli support needs to be enabled.

* Update docker.sh

* Use docker cli with experimental cli support enabled only when needed

.travis/docker.sh

@@ -15,6 +15,8 @@ build_and_push() {
 }
 
 push_manifest() {
+  export DOCKER_CLI_EXPERIMENTAL=enabled  
+
   docker manifest create $DOCKER_USERNAME/zigbee2mqtt:latest$1 $DOCKER_USERNAME/zigbee2mqtt:latest$1 $DOCKER_USERNAME/zigbee2mqtt:arm32v6$1 $DOCKER_USERNAME/zigbee2mqtt:arm64v8$1
 
   docker manifest annotate $DOCKER_USERNAME/zigbee2mqtt:latest$1 $DOCKER_USERNAME/zigbee2mqtt:arm32v6$1 --os linux --arch arm --variant v6
@@ -25,6 +27,8 @@ push_manifest() {
   docker manifest push -p $DOCKER_USERNAME/zigbee2mqtt:latest$1
 
   docker run --rm mplatform/mquery $DOCKER_USERNAME/zigbee2mqtt:latest$1
+
+  export DOCKER_CLI_EXPERIMENTAL=disabled
 }
 
 # Only update Docker images for: