qemu.cfg: Update KSM query_regex for check KSM status

Update the query_regex for check KSM status for RHEL 5 host.
The old one is out of date, and can not work any more.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: fix die() not response in ksm_overcommit.ksm_serial

After we kill the previous guest. We still need wait the command line
finish in the last guest. Also need send the die() command in the session
for the last vm.

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