Instead of mucking around with the awful iscsi target names we're
stuck with, just go ahead and rescan all the LUNs. There doesn't seem to
be a difference in the delay between rescanning a signal target versus
all targets (almost none).

Also, the previous version failed to include the instructions to
rescan/resize on *all* the cluster nodes, because that doesn't happen
automatically and if the instance is happens to be restarted on another
node, it could fail to boot or worse, cause io errors.