fix(Makefile): dockerize the unit test command

note that DEV_ENV_PREFIX_CGO_ENABLED was added because —race requires
cgo to be enabled

Author: Aaron Schlesinger

Makefile

@@ -13,6 +13,7 @@ endif
 DEV_ENV_IMAGE := quay.io/deis/go-dev:0.9.0
 DEV_ENV_WORK_DIR := /go/src/${repo_path}
 DEV_ENV_PREFIX := docker run --rm -e GO15VENDOREXPERIMENT=1 -e CGO_ENABLED=0 -v ${CURDIR}:${DEV_ENV_WORK_DIR} -w ${DEV_ENV_WORK_DIR}
+DEV_ENV_PREFIX_CGO_ENABLED := docker run --rm -e GO15VENDOREXPERIMENT=1 -e CGO_ENABLED=1 -v ${CURDIR}:${DEV_ENV_WORK_DIR} -w ${DEV_ENV_WORK_DIR}
 DEV_ENV_CMD := ${DEV_ENV_PREFIX} ${DEV_ENV_IMAGE}
 DIST_DIR := _dist
 
@@ -96,4 +97,4 @@ test-style:
 	done
 
 test-unit:
-	$(GOTEST) $(shell glide novendor)
+	${DEV_ENV_PREFIX_CGO_ENABLED} ${DEV_ENV_IMAGE} ${GOTEST} $$(glide nv)