Convert build.sh to a multi-stage Dockerfile. (#452)

environments/binary/builder/Dockerfile

@@ -0,0 +1,4 @@
+ARG BUILDER_IMAGE=fission/builder:latest
+FROM ${BUILDER_IMAGE}
+
+ADD build.sh /usr/local/bin/build

environments/binary/builder/build.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+apk update
+
+CWD=$(pwd)
+
+if [ -f ${SRC_PKG}/build.sh ]; then
+    cd ${SRC_PKG}
+    ./build.sh
+    cd ${CWD}
+fi
+
+cp -rf ${SRC_PKG} ${DEPLOY_PKG}