qemu.tests: update drive_mirror test cfg

Update drive_mirror test configuration to make it stablly

changes from v1:
    fix some coding style issue

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: add steps to install stress app if not installed

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: move snapshot image to image dir

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: update block copy test configuration

Update configuration to make test works stably

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: update config filter some qemu images case

use "no raw qed vmdk" instead "only qcow2" because new image format (eg. qcow3)
maybe support in futuer;

Signed-off-by: Xu Tian <xutian@redhat.com>
virttest:new interface to clear a kind of events

We need to clear a kind of event only before send a monitor command, and
jude the command go into effect by check event; This interface used to
clear this kinds of events in events list;

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: fix incorrect test steps in qemu_img.rebase test

qemu-img rebase function used to changes backing_file and backing_file
format for an image file;
In this case, we create snapshots "base->sn1->sn2", then rebase sn2's backing_file
to base, then bootup with sn2 and check sn2's backing_file is base;

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: correct configuration for qemu_img tests

image rebase only support by qcow2 and qed image format; commit is used
to commit connect to image's backingfile;And boot from converted qed format
image is not support RHEL qemu;

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: remove duplicated function in block_copy module

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: refactor block_stream test with exist framework

changes from v1:
    use utils_misc.get_qemu_img_binary() to get qemu-img binary path
    instead re.search() with re.findall()

Signed-off-by: Xu Tian <xutian@redhat.com>