6637 replacing "dontclose" with "should_close"

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: David Schwartz <dschwartz783@gmail.com>

illumos/illumos-gate@d189620258b3c9b0e2f7e2104840be2eee7c68e5