block: Prevent sleeping jobs from resuming if they have been paused

If we pause a block job and drain its BlockDriverState we want that
the job remains inactive until we call block_job_resume() again.

However if we pause the job while it is sleeping then it will resume
when the sleep timer fires.

This patch prevents that from happening by checking if the job has
been paused after it comes back from sleeping.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 3d9011151512326b890d22bdab3530244ef349d7.1464346103.git.berto@igalia.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
