Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - python34_update: Updated build scripts for Centos and RHEL to python34

    Recent patch update to collectd requires new packages that must
    have python34 as a minimum version available. This updates the
    build scripts for Centos and RHEL to use scl enabled python34.

    1. Adds needed packages to build correctly for Centos and RHEL
    2. Changes repo location to pull scl enabled python34
    3. Modifies enablement of scl to new package string
    4. Updates documentation to reflect change

    JIRA: VSPERF-558

    Change-Id: I52257ecfc6abc2112c30137c1de3ced272f21066
    Signed-off-by: Christian Trautman <ctrautma@redhat.com>