Add parallelism to cross build

Reusable docker engine

Signed-off-by: Daniel Nephin <dnephin@docker.com>

dockerfiles/Dockerfile.cross

@@ -1,18 +1,2 @@
-
-FROM    golang:1.8.3
-
-# allow replacing httpredir or deb mirror
-ARG     APT_MIRROR=deb.debian.org
-RUN     sed -ri "s/(httpredir|deb).debian.org/$APT_MIRROR/g" /etc/apt/sources.list
-
-RUN     apt-get update -qq && apt-get install -y -q \
-            libltdl-dev \
-            gcc-mingw-w64 \
-            parallel \
-            ;
-
-COPY    dockerfiles/osx-cross.sh /tmp/
-RUN     /tmp/osx-cross.sh
-ENV     PATH /osxcross/target/bin:$PATH
-
+FROM    dockercore/golang-cross@sha256:d24e7affa3a85d460d2303c2549f03fc866f2b97d771ccf07b0e6e2b411dd207
 WORKDIR /go/src/github.com/docker/cli

dockerfiles/osx-cross.sh

@@ -1,29 +0,0 @@
-#!/usr/bin/env bash
-#
-# Install dependencies required to cross compile osx, then cleanup
-#
-# TODO: this should be a separate build stage when CI supports it
-
-
-set -eu -o pipefail
-
-PKG_DEPS="patch xz-utils clang"
-
-apt-get update -qq
-apt-get install -y -q $PKG_DEPS
-
-OSX_SDK=MacOSX10.11.sdk
-OSX_CROSS_COMMIT=a9317c18a3a457ca0a657f08cc4d0d43c6cf8953
-OSXCROSS_PATH="/osxcross"
-
-echo "Cloning osxcross"
-time git clone https://github.com/tpoechtrager/osxcross.git $OSXCROSS_PATH
-cd $OSXCROSS_PATH
-git checkout -q $OSX_CROSS_COMMIT
-
-echo "Downloading OSX SDK"
-time curl -sSL https://s3.dockerproject.org/darwin/v2/${OSX_SDK}.tar.xz \
-    -o "${OSXCROSS_PATH}/tarballs/${OSX_SDK}.tar.xz"
-
-echo "Building osxcross"
-UNATTENDED=yes OSX_VERSION_MIN=10.6 ${OSXCROSS_PATH}/build.sh > /dev/null