virttest: Add vm process status for image process functions

Let the image check process can get if vm process is still running. Some
options in image like lazy_refcounts improve the performance but do not
support image check while the qemu process still running. Also make this
can be control by cfg file.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
virttest: Add a parameter to skip cluster leak warning in image check

When the guest is running we should not raise error in image check if
it is only a cluster leak warning. And add it as a parameter in base.cfg
so people can igonre the warning message if they do not care about it in
their tests.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #1573 from ypu/image_check

Some image check improve for env_process