Update git submodules

Update git submodules

* Update docs/submodules/samplevnf from branch 'master'
  - Merge "docs: Update install and release docs for DPDK migration support"
  - docs: Update install and release docs for DPDK migration support

    JIRA: SAMPLEVNF-48

    Updating INSTALL.rst and RELEASE_NOTES.rst for DPDK migration
    support. The additional files are created to make it as per the
    opnfv document standard to generate the html files.

    Change-Id: I4b0af4c3afeef91fc806285b02c0ce47d61ebfbd
    Signed-off-by: Anand B Jyoti <anand.b.jyoti@intel.com>