Extend TC008 to run pktgen-dpdk inside VM

Extend TC008 to run pktgen-dpdk inside VM
Need a fast path inside VM to verify full throughput of SRIOV and OVS-dpdk.

Update 1: Change newly added file names to avoid conflict
Update 2: Add more unit test cases
Update 3: Fix default parameter typo for testpmd
Update 4: Adapted to the pktgen-dpdk prompt change from "Pktgen>" to "Pktgen:/>", now just expect "Pktgen"
Update 5: Per comment, merge common functions between latency and throughput tests to utils.py
Update 6: Per comment, seperate the test case from TC008 to a new test case TC077

Change-Id: I1f7471d4ba77636a3a66c79c2652578321312185
JIRA: YARDSTICK-614
Signed-off-by: Jing Zhang <jing.c.zhang@nokia.com>