tests.guest_suspend: Fix the wrong separator for cpu flags

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu: Reset image_extra_params parameter in some block tests.

These tests will create some other format of image, so the
options for qcow3 would affect them.
To make these cases still work with qcow3 format, reset the
'image_extra_params' parameter in them.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
tests.boot_savevm: Get parameters with new method in virt-test

If the parameters are missing, just skip this test.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Merge pull request #592 from zhouqt/minor-fix

qemu: Minor fixes for qemu test cases