qemu-iotests: Drop local version of cancel_and_wait from 040

iotests.py already has one.

Signed-off-by: Fam Zheng <famz@redhat.com>
blkdebug: add "remove_break" command

This adds "remove_break" command which is the reverse of blkdebug
command "break": it removes all breakpoints with given tag and resumes
all the requests.

Signed-off-by: Fam Zheng <famz@redhat.com>
qemu-iotest: Add pause_drive and resume_drive methods

They wrap blkdebug "break" and "remove_break".

Add optional argument "resume" to cancel_and_wait().

Signed-off-by: Fam Zheng <famz@redhat.com>
qemu-iotests: Make test case 030, 040 and 055 deterministic

Pause the drive and start the block job, so we won't miss the block job.

Signed-off-by: Fam Zheng <famz@redhat.com>