MAINTAINERS: Add jcody as blockjobs, block devices maintainer

MAINTAINERS: Add jcody as blockjobs, block devices maintainer

The block layer maintainership is being split up into smaller, more
manageable pieces.

I propose that I take over / assist with the following areas:

    * blockjobs
    * archipelago
    * curl
    * gluster
    * nfs
    * rbd
    * sheepdog
    * ssh
    * vhdx

As John Snow noted in a different patch:

As we split out the block layer, we will begin using the qemu-block
mailing list as a catchall for all of the block layer subcomponents.
Please CC qemu-block@nongnu.org for all block layer patches, including
any that touch the above listed areas.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>