illumos gate

This is a bit odd; it is still possible we can get non-labeled lofi entry from device name cache, so we need to check the name and keep waiting if the name type is wrong (till we hit timeout).

Increase the timeout from 30 to 120 (because lofiadm is waiting for devfsadm symlinks for 120s), and add cv_broadcast to notify about device removal.

Testing done: did loop lofiadm -a, -d -la -d sequence 100 times, observed with dtrace that indeed, we sometimes do get /dev/rlofi entries, but lofiadm did not error out any more.