Update git submodules

Update git submodules

* Update docs/submodules/appc.git from branch 'master'
  to 389393eb86e4325f3fcc7cd6b4135be2881b0baa
  - optimize size and time using "--no-cache-dir"

    Using "--no-cache-dir" flag in pip install ,make sure dowloaded packages
    by pip don't cached on system . This is a best practise which make sure
    to fetch ftom repo instead of using local cached one . Further , in case
    of Docker Containers , by restricing caching , we can reduce image size.
    In term of stats , it depends upon the number of python packages
    multiplied by their respective size . e.g for heavy packages with a lot
    of dependencies it reduce a lot by don't caching pip packages.

    Further , more detail information can be found at

    https://medium.com/sciforce/strategies-of-docker-images-optimization-2ca9cc5719b6

    Issue-ID: APPC-1887

    Signed-off-by: Pratik Raj <rajpratik71@gmail.com>
    Change-Id: Iaf92c95eae404706828c346ac02cf0f63c71f5e2