blockjob: Add permissions to block_job_add_bdrv()

blockjob: Add permissions to block_job_add_bdrv()

Block jobs don't actually do I/O through the the reference they create
with block_job_add_bdrv(), but they might want to use the permisssion
system to express what the block job does to intermediate nodes. This
adds permissions to block_job_add_bdrv() to provide the means to request
permissions.

Signed-off-by: Kevin Wolf <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Acked-by: Fam Zheng <[email protected]>