qemu.tests: Add a new subtest multi_nics_verify

Verify guest NIC numbers again whats provided in test config file.
If the guest NICs info does not match whats in the params at first,
try to tune up the config file and reboot and then verify again.

Signed-off-by: Ken Cao <kcao@redhat.com>
Signed-off-by: Yolkfull Chow <yzhou@redhat.com>
qemu.tests: add case virtual_nic_private support

This patch add case virtual nic private support.

change log:
    Change from V1:
        1.add parameters list
        2.delete some default values.
        3.close all sessions after test
        4.make more detailed loginfo.
    Change from V2
        1.modify dd command add oflag=direct
        2.using try..finally to catch exception
    change from V3:
        1.modify data case method, using tcpdump -c to control.
        2.add -i option for tcpdump cmd.
    change from V4:
        1.add new mon funcution.
        2.add more debuginfo
    change from V5:
        1.modify the function data_mon, using only on thread
        2.modify coding style
    change from V6:
        1.modify coding style
        2.modify some typo
        3.add judgement before close the session
Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
Acked-by: Feng Yang <fyang@redhat.com>
qemu.tests: add test bigfile transfer via ipv6

This patch add virtual nic test transfer bigfile via ipv6

ChangeLog:
     Change form V1:
         1. using linklocal address
         2. modify error context
     Change from V2:
         1. clear test tmp file
         2. close the guest session
     Change from V3:
         1. using try finally to clear test tmp file
     Change form V4:
         1. remove unused module uuid
         2. add md5sum check in every step.
     Change form V5:
         1. modify dd_cmd default value
     change from V6:
         1. modify TestError to TestFail
     change from V7:
         1. add timeout for filetransfer and md5check.
     change form V8:
         1. modify the coding style.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
Acked-by: Xu Tian <xutian@redhat.com>