Allow specifying Docker image to use for building

build.sh

@@ -123,11 +123,12 @@ case "${1:-default}" in
 		;;
 
 	docker-all)
+		img=${DOCKERIMG:-syncthing/build:latest}
 		docker run --rm -h syncthing-builder -u $(id -u) -t \
 			-v $(pwd):/go/src/github.com/syncthing/syncthing \
 			-w /go/src/github.com/syncthing/syncthing \
 			-e "STTRACE=$STTRACE" \
-			syncthing/build:latest \
+			"$img" \
 			sh -c './build.sh clean \
 				&& ./build.sh test-cov \
 				&& ./build.sh bench \
@@ -135,11 +136,12 @@ case "${1:-default}" in
 		;;
 
 	docker-test)
+		img=${DOCKERIMG:-syncthing/build:latest}
 		docker run --rm -h syncthing-builder -u $(id -u) -t \
 			-v $(pwd):/go/src/github.com/syncthing/syncthing \
 			-w /go/src/github.com/syncthing/syncthing \
 			-e "STTRACE=$STTRACE" \
-			syncthing/build:latest \
+			"$img" \
 			sh -euxc './build.sh clean \
 				&& go run build.go -race \
 				&& export GOPATH=$(pwd)/Godeps/_workspace:$GOPATH \
@@ -149,21 +151,23 @@ case "${1:-default}" in
 		;;
 
 	docker-lint)
+		img=${DOCKERIMG:-syncthing/build:latest}
 		docker run --rm -h syncthing-builder -u $(id -u) -t \
 			-v $(pwd):/go/src/github.com/syncthing/syncthing \
 			-w /go/src/github.com/syncthing/syncthing \
 			-e "STTRACE=$STTRACE" \
-			syncthing/build:latest \
+			"$img" \
 			sh -euxc 'go run build.go lint'
 		;;
 
 
 	docker-vet)
+		img=${DOCKERIMG:-syncthing/build:latest}
 		docker run --rm -h syncthing-builder -u $(id -u) -t \
 			-v $(pwd):/go/src/github.com/syncthing/syncthing \
 			-w /go/src/github.com/syncthing/syncthing \
 			-e "STTRACE=$STTRACE" \
-			syncthing/build:latest \
+			"$img" \
 			sh -euxc 'go run build.go vet'
 		;;