block/mirror: honor ratelimit again

block/mirror: honor ratelimit again

Commit b76e4458b1eb3c32e9824fe6aa51f67d2b251748 ("block/mirror: change
the semantic of 'force' of block-job-cancel") accidentally removed the
ratelimit in the mirror job.

Reintroduce the ratelimit but keep the block-job-cancel force=true
behavior that was added in commit
b76e4458b1eb3c32e9824fe6aa51f67d2b251748.

Note that block_job_sleep_ns() returns immediately when the job is
cancelled.  Therefore it's safe to unconditionally call
block_job_sleep_ns() - a cancelled job does not sleep.

This commit fixes the non-deterministic qemu-iotests 185 output.  The
test relies on the ratelimit to make the job sleep until the 'quit'
command is processed.  Previously the job could complete before the
'quit' command was received since there was no ratelimit.

Cc: Liang Li <liliang.opensource@gmail.com>
Cc: Jeff Cody <jcody@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20180424123527.19168-1-stefanha@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>