Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "load_gen: Supporting loading of load_gen via loader."
  - load_gen: Supporting loading of load_gen via loader.

    Currently all tools are loaded via loader utility, except load_gen.
    Load_gens were loaded directly through component_factory.
    This patch adds support to load load_gens through loader utility.

    The changes are as follows:
    1. Configuration changes:The common.conf include configuration of
       directory. testcases.conf includes changes to load configuration,
       where tool is no more part of the load-configuration. The
       custom.conf has configuration of LOADGEN to be used - this configuration
       replaces the earlier 'tool' configuration parameter.
    2. loader_utility_changes:  In loader.py, loadgen_loader is
       defined, which is used in new get_loadgen function.
    3. component_factory changes: in create_loadgen, similar
       to other tools, the function just retuns the object of loadgen_class.
    4. Renaming of Dummy load_gen: Loader fails to load properly a dummy
       loadgen due to name-clash with dummy in pkt_gen. To avoid this name clash
       dummy is renamed to dummyloadgen.
    5. testcase changes: create_loadgen is now called with output of
       loader's get_loadgen_class.
    6. Fixed Pylint Errors and extra-space at the end.
    7. Included CLI options support for --loadgen and --list-loadgens.
       Thanks to Martin K.
    8. Added the missing loadgen parameter in testcases.conf.
    9. Fixed the missing comma error.
    10. Added CI change in build-vsperf.sh
    11. Fixed configuration reading in stress/stress.py

    JIRA: VSPERF-533

    Change-Id: I3fbb259618825a12fef55320a748a4f02509190b
    Signed-off-by: Sridhar K. N. Rao <sridhar.rao@spirent.com>
    Signed-off-by: Martin Klozik <martinx.klozik@intel.com>