qemu.tests: Add check for qemu process after quit()

We need check the qemu process can quit normally in the end of test.
Also fix the memory size inside script and remove the useless parameters.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #168 from ypu/valgrind

qemu.tests: Add check for qemu process after quit()