qemu.tests: Add new case timedrift montonicity

Add new case timedrift_monotonicity.py
and check the guest time monotonicity after migration.
There are two case:
1. Take the guest time during migration and check time.
2. Let guest running long time after migration and
   check the time.

change from v1:
1. delete guest script, add function to get time in test case
2. fix typo

change from v2:
1. add cmd_timeout
2. add parameter for function get_time()

Signed-off-by: Golita Yue <gyue@redhat.com>
Acked-by: Qingtang Zhou <qzhou@redhat.com>
Acked-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: Add timedrift with cpu online/offline test case.

Add timedrift with cpu online/offline test case.
 Check the guest time after offline the cpu
 Check the guest time after online the cpu

change from v1:
1. fix typo
2. add more error.context for other steps

Signed-off-by: Golita Yue <gyue@redhat.com>
qemu.tests.timedrift_with_stop: Add functions for stopping qemu with signal

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Acked-by: Feng Yang<fyang@redhat.com>
Acked-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: add kernel boot options for timedrift

changes from v1:
 - add boot options for remove.

changes from v2:
 - also fix guest kernel cmdline in other timedrift testcases.

changes from v3:
 - add a judgement for boot options, don't run this step if there
   is nothing to be add or remove

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Acked-by: Feng Yang <fyang@redhat.com>
Acked-by: Suqin Huang<shuang@redhat.com>
qemu.tests: Measure increment of clock drift (100% load)

Add two parameters to let test case timedift.with_load
can be configured. When need run long time testing, can
reset the value "test_duration" & "interval_gettime".

Signed-off-by: Golita Yue <gyue@redhat.com>