qemu.tests: Add base KSM test case

Add three KSM test:
    - Negative test for ksm
    - KSM per vm
    - Merging and Splitting in one vm

All this three test needs the following steps:
1. Get and set the env parameters for KSM
2. Boot up guest with proper command line
3. Set env inside of guest
4. Allocate 0 pages to make the KSM run
5. Allocate different pages to get split of the pages(option for
   different cases)
6. Result check and env reset

change from v1:
    - add the host depended parameters in cfg file
    - use os.system to restart ksmtund as commands will wait the
      return value.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>

This patch fix the problem caused by the sciprt have move to
another dir. So modify the path of the file.

Signed-off-by: yunzheng <yunzheng@redhat.com>

Fix reference problem

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>

Update API using in ksm_base to date

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Signed-off-by: Feng Yang <fyang@redhat.com>

Set up the memory filled in guest lower that the free memory in guest.
To ignore the OOM killer.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>