OS-2197 renaming dynamic sdev nodes leads to panic
OS-2195	sdev dynamic directories can be created multiple times
OS-2137 sdev vfs refcount assertion violation
OS-2118 chmod 700 /dev/zcons/* panics the box
OS-2311 sdev could use some theory statements
Reviewed by: Keith M Wesolowski <wesolows@foobazco.org>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>