Don't shadow read(2) definition with read argument in vdev_{create,probe}

This fixes several -Wshadow warnings introduced in r192194, but now errors
with gcc 6.3.0.

MFC after: 3 days
Reported by: amd64-gcc-6.3.0 (devel/amd64-xtoolchain-gcc)
Sponsored by: Dell EMC Isilon