vsperf: Enhanced vswitchperf configuration

vsperf: Enhanced vswitchperf configuration

Original implementation of vsperf specific class
was changed to relfect recent vsperf changes. It is
now possible to modify any of vsperf's configuration
parameters via --test-param CLI argument. It means, that
it is possible to write a yardstick TC, which will define
all required vsperf configuration inside the YAML TC
definition.
Vsperf documentation related to yardstick usage and
sample TC files are located inside vsperf repository
and they were updated by a separate patch.

JIRA: VSPERF-422

Change-Id: I978d1c85ffeb3c90d9d47a20c6c0e0f68b437123
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: <sunshine.wang@huawei.com>
Reviewed-by: <lvjing5@huawei.com>
Reviewed-by: <jean.gaoliang@huawei.com>
Reviewed-by: <david.j.chou@intel.com>