Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "loadgen: Support for Stressor-VMs as a Loadgen"
  - loadgen: Support for Stressor-VMs as a Loadgen

    This patch adds support for stressor-VMs as a loadgen in VSPERF.
    The changes include:
    1. 07_loadgen.conf: User can specify the stressor-VM specific
    configuration. It includes, image-name, path, nics, memory, etc.
    2. loadgen/stressorvm/stressor_vm.py: This file implement ILoadGenerator
    interface. It implements all the necessary APIs for starting and
    stopping the loads.
    3. Fixed Pylint Error
    4. Removed the network device configuration from qemu-system-x86_64
    command as stessor-vm mostly focus on CPU and memory stressing.
    5. Moved the creation of loadgen after the VNFs are setup in
    testcase.py.
    6. Fixed copyright issues.
    7. Removed python-3 checking. Improved exception handling
    8. Set Default loadgen as DummyLoadGen
    9. Improved OSError Printing with directory name and error
    10. Update the year in license. 2017-2018.

    JIRA: VSPERF-504

    Change-Id: Iad6c0780c184f8e36eddcbcae2a580f41118e8dc
    Signed-off-by: Sridhar K. N. Rao <sridhar.rao@spirent.com>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index 7a1a6fb..b8ef508 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit 7a1a6fb5d55cb0b5463408730f0778add4549be9
+Subproject commit b8ef508a78181e017071d9189bb0030305fd1080