infra/image/shcontainer: Volume support and new container_tee

This change adds support for volumes to container_create. Now it can be
used like in this example:

    container_create "${name}" "${local_image}" "hostname=${hostname}" \
        "${capabilities:+capabilities=$capabilities}" \
        volume=$PWD:/root/src

The new function container_tee has been added to enable creation of
fiiles with content from stdin like in this example:

    cat <<EOF | container_tee "${name}" "/root/.gdbinit"
    set debuginfod enabled on
    set follow-fork-mode child
    EOF