MAINTAINERS: Remove myself as block maintainer

MAINTAINERS: Remove myself as block maintainer

I'll not be involved in day-to-day qemu development.  Remove myself as
maintainer from the remainder of the network block drivers, and revert
them to the general block layer maintainership.

Move 'sheepdog' to the 'Odd Fixes' support level.

For VHDX, added my personal email address as a maintainer, as I can
answer questions or send the occassional bug fix.  Leaving it as
'Supported', instead of 'Odd Fixes', because I think the rest of the
block layer maintainers and developers will upkeep it as well, if
needed.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Acked-by: Max Reitz <mreitz@redhat.com>
Message-Id: <63e205cb84c8f0a10c1bc6d5d6856d72ceb56e41.1537984851.git.jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>