Make AUFS optional and ship choice of kernels

This seems the best option, although none are great

- build with `make AUFS=1` to build with AUFS support, currently with 4.8 kernel
- default is to build without AUFS support, with 4.9 kernel

This recognises that AUFS supprot is temporary #620 and only there until
we can phase it out on desktop editions, and allow the other editions that
never shipped with AUFS to ship something very close to mainline.

However we do still apply the patches so that the non AUFS branch runs fine on
all platforms, so it can be tested elsewhere.

We may be able to move the kernel versions back in line when 4.9 aufs support is out.

Plan is to shift CI to build both sets of images, and get the Desktop editions to
pick up the aufs set automatically, once this is merged.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

alpine/kernel/Dockerfile

@@ -1,7 +1,7 @@
 # Tag: 36aecb5cf4738737634140eec9abebe1f6559a39
 FROM mobylinux/alpine-build-c@sha256:d66b9625abc831f28f8c584991a9cb6975e85d3bb3d3768474b592f1cf32a3a6
 
-ARG KERNEL_VERSION=4.8.14
+ARG KERNEL_VERSION=4.9
 
 ENV KERNEL_SOURCE=https://www.kernel.org/pub/linux/kernel/v4.x/linux-${KERNEL_VERSION}.tar.xz
 
@@ -9,42 +9,6 @@ RUN curl -fsSL -o linux-${KERNEL_VERSION}.tar.xz ${KERNEL_SOURCE}
 
 RUN cat linux-${KERNEL_VERSION}.tar.xz | tar --absolute-names -xJ &&  mv /linux-${KERNEL_VERSION} /linux
 
-# this is aufs4.8 20161010
-ENV AUFS_REPO       https://github.com/sfjro/aufs4-standalone
-ENV AUFS_BRANCH     aufs4.8
-ENV AUFS_COMMIT     e9fd128dcb16167417683e199a5feb14f3c9eca8
-
-# Download AUFS
-RUN git clone -b "$AUFS_BRANCH" "$AUFS_REPO" /aufs && \
-    cd /aufs && \
-    git checkout -q "$AUFS_COMMIT"
-
-# aufs-util 20151116
-ENV AUFS_TOOLS_REPO https://github.com/ncopa/aufs-util.git
-ENV AUFS_TOOLS_COMMIT 3b7c5e262b53598a8204a915e485489c46d4e7a4
-
-# Download aufs tools
-RUN git clone ${AUFS_TOOLS_REPO} && \
-    cd /aufs-util && \
-    git checkout "$AUFS_TOOLS_COMMIT" 
-
-#BUILD
-# patch kernel with aufs
-RUN cd /linux && \
-    cp -r /aufs/Documentation /linux && \
-    cp -r /aufs/fs /linux && \
-    cp -r /aufs/include/uapi/linux/aufs_type.h /linux/include/uapi/linux/ && \
-    set -e && for patch in \
-        /aufs/aufs*-kbuild.patch \
-        /aufs/aufs*-base.patch \
-        /aufs/aufs*-mmap.patch \
-        /aufs/aufs*-standalone.patch \
-        /aufs/aufs*-loopback.patch \
-        /aufs/lockdep-debug.patch \
-    ; do \
-        patch -p1 < "$patch"; \
-    done
-
 COPY kernel_config /linux/arch/x86/configs/x86_64_defconfig
 COPY kernel_config.debug /linux/debug_config
 
@@ -72,12 +36,4 @@ RUN make INSTALL_MOD_PATH=/tmp/kernel-modules modules_install && \
     ( cd /tmp && tar cf /kernel-headers.tar include ) && \
     ( cd /tmp/kernel-modules && tar cf /kernel-modules.tar . )
 
-# Build aufs tools, do this here as they need kernel headers and to match aufs
-# Fortunately they are built statically linked
-RUN cd /aufs-util && \
-    CPPFLAGS="-I/tmp/include" CFLAGS=$CPPFLAGS LDFLAGS=$CPPFLAGS make && \
-    DESTDIR=/tmp/aufs-utils make install && \
-    rm -rf /tmp/aufs-utils/usr/lib /tmp/aufs-utils/usr/share && \
-    cd /tmp/aufs-utils && rm libau* && tar cf /aufs-utils.tar .
-
-RUN printf "KERNEL_SOURCE=${KERNEL_SOURCE}\nAUFS_REPO=${AUFS_REPO}\nAUFS_BRANCH=${AUFS_BRANCH}\nAUFS_COMMIT=${AUFS_COMMIT}\nAUFS_TOOLS_REPO=${AUFS_TOOLS_REPO}\nAUFS_TOOLS_COMMIT=${AUFS_TOOLS_COMMIT}\n" > /kernel-source-info
+RUN printf "KERNEL_SOURCE=${KERNEL_SOURCE}\n" > /kernel-source-info