vpp: Initial support of VPP vSwitch

vpp: Initial support of VPP vSwitch

Support of VPP was implemented into VSPERF. Initial implementation
uses step driven testcases to configure P2P, PVP and PVVP network
scenarios. These testcases were prepared for three RFC2544 traffic
types, i.e. throughput, continuous stream and back to back.
VPP configuration is driven by new configuration option VSWITCH_VPP_ARGS.
It is possible to use three types of l2 port connection supported
by VPP, i.e. l2 xconnect (default), l2patch and l2 bridge features.
Configuration is driven by parameter VSWITCH_VPP_L2_CONNECT_MODE.

JIRA: VSPERF-495

Change-Id: Idebef9b10fb0d70796adb3405fec77302de00a7e
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>