yardstick: Documentation and YAML testcase definitions

yardstick: Documentation and YAML testcase definitions

Yardstick supports execution of vsperf specific testcases.
These testcases are specified by YAML files located
inside yardstick/tests directory. Documentation describing
yardstick usage and execution of vsperf testcases is
part of the userguide.

JIRA: VSPERF-288

Change-Id: I5a575d28d344e0f3e0a1c8434e2f3231fd312d31
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Maryam Tahhan <maryam.tahhan@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: <bmichalo@redhat.com>
Reviewed-by: <sridhar.rao@spirent.com>