Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "pylint: Add pylint into requirements.txt"
  - pylint: Add pylint into requirements.txt

    Pylint installation was part of vsperf installation scripts, which is
    not following vsperf generic approach to add all required python
    packages into requirements.txt. It also means, that the same
    version of pylint is used for verification of all patches at given
    server. This is causing issues in case, that different versions
    of pylint are required to verify vsperf code, e.g. older version
    might be required to verify patches of previous OPNFV release.

    Pylint with exact version number was added into requirements.txt,
    so correct version of pylint is used for verification of vspef code.

    JIRA: VSPERF-563

    Change-Id: I48c9cacd87f016e6047ed965728d3b8d63e6461f
    Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
    Reviewed-by: Al Morton <acmorton@att.com>
    Reviewed-by: Christian Trautman <ctrautma@redhat.com>
    Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
    Reviewed-by: Richard Elias <richardx.elias@intel.com>