sdk_container: fix submodules parent path in container

Signed-off-by: Thilo Fromm <thilo@kinvolk.io>

run_sdk_container

@@ -103,6 +103,8 @@ if [ -z "$stat" ] ; then
     docker create $tty -i \
        -v /dev:/dev \
        -v "$(pwd)/sdk_container:/mnt/host/source/" \
+       -v "$(pwd)/sdk_container/git-override/.git-coreos-overlay:/mnt/host/source/src/third_party/coreos-overlay/.git" \
+       -v "$(pwd)/sdk_container/git-override/.git-portage-stable:/mnt/host/source/src/third_party/portage-stable/.git" \
        -v "$(pwd)/__build__/images:/mnt/host/source/src/build" \
        -v "$(pwd):/mnt/host/source/src/scripts" \
        $gpg_volumes \

sdk_container/git-override/.git-coreos-overlay

@@ -0,0 +1 @@
+gitdir: ../../scripts/.git/modules/sdk_container/src/third_party/coreos-overlay

sdk_container/git-override/.git-portage-stable

@@ -0,0 +1 @@
+gitdir: ../../scripts/.git/modules/sdk_container/src/third_party/portage-stable

sdk_container/git-override/README.md

@@ -0,0 +1,5 @@
+# GIT overrides for submodules
+
+In the SDK container, the scripts root is at a different relative path to the submodules.
+The overrides in this directory are into coreos-overlay/.git and portage-stable.gitso the submodules find itheir parents.
+