Handle build environment variables for proxy access (#755)

cluster/images/provider-aws/Makefile

@@ -24,7 +24,7 @@ include ../../../build/makelib/imagelight.mk
 img.build:
 	@$(INFO) Family base image to build: $(IMAGE)
 	@$(INFO) Building image $${IMAGE}; \
-	$(MAKE) BUILD_ARGS="--load" IMAGE=$${IMAGE} XPKG_REG_ORGS=$(XPKG_REG_ORGS) img.build.shared; \
+	$(MAKE) BUILD_ARGS="--load ${BUILD_ARGS}" IMAGE=$${IMAGE} XPKG_REG_ORGS=$(XPKG_REG_ORGS) img.build.shared; \
 	if [[ "$${LOAD_MONOLITH}" == "true" ]]; then \
 	  $(MAKE) batch-process SUBPACKAGES=monolith BATCH_PLATFORMS=$(PLATFORM) BUILD_ONLY=true STORE_PACKAGE=monolith && \
 	  export t=$$(docker load -qi "$(XPKG_OUTPUT_DIR)/$(PLATFORM)/$(PROJECT_NAME)-monolith-$(VERSION).xpkg") && \