virttest: Destory pre vm in env_process

Destory the pre vm in preprocess_vm. otherwise some strange error
will be produced as some vm object options is different.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests.virtual_nic_send_buffer: Update the way used to checkout md5 in guest

md5 command in guest may have different output format. It is a little difficult to
filter out the md5 value from the output. So just checkout whether correct md5 value
is in the output is enough.

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests: Bug fix about drift for timedrift_with_stop

kvm guests CLOCK_MONOTONIC not count when guest is paused,
so drift need to subtract stop_time.

starting from Win2012 Windows no longer relies on number of
injected RTC interrupts for time keeping, and the time drift
is seen because "stop" monitor command also stops PM timer,
so this is unsupported scenario from Win2012 and disabled this
case from Win2012.

changes from v1:
    add some comments for windows guest.
changes from v2:
    add check rtc_clock for windows
changes from v3:
    add new scenario rtc_clock = host and rtc_clock = vm for this case.

Signed-off-by: Shuping Cui <scui@redhat.com>
qemu.tests: bug fix for timedrift_with_cpu_offline

add stop_time after set cpu offline, and update "smp_min" to "smp"
in config file.

changes from v1:
    drift_threshold type fix

Signed-off-by: Shuping Cui <scui@redhat.com>
Merge pull request #1290 from FengYang/virtual_nic_send_buffer

qemu.tests.virtual_nic_send_buffer: Update the way used to checkout md5 ...
tests.jumbo: Modify cfg of jumbo tests.

For windows guest when using e1000 the max icmp size is not
"jumbopacket - 28", but "jumbopacket - 42", so modify the cfg.

This patch also modify the coding style to up to the pep8.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
tests.jumbo: make jumbo test support macvtap

This patch make jumbo test support macvtap. when using macvtap nic,
before chang the mtu of the macvtap, must change the base interface
mtu.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
block_resize.cfg: RHEL5 need reboot step in block_resize case

Guest RHEL5 could not detect disk change, assign need_reboot
as yes in the cfg file. And disable RHEL.4 guest.

history:
  V3:
    add no filter for RHEL.4 guest
  V2:
    change to RHEL.5 condition
  V1:
    add RHEL and 5 condition lines

Signed-off-by: Xiangmin Han <xhan@redhat.com>
Merge pull request #1140 from ypu/restart_vm

virttest: Should destroy pre vm in create()
Merge pull request #1279 from Xiangmin/block_resize_bugfix

block_resize.cfg: RHEL5 need reboot step in block_resize case
Merge pull request #1229 from spcui/timedrift

qemu.tests.timedrift_with_stop: Bug fix about drift
Merge pull request #1185 from humanux/jumbo

tests.jumbo: Modify cfg of jumbo tests.