Allow GetSomeSpace_r to select an optimal host

Allow GetSomeSpace_r to select an optimal host

Previously GetSomeSpace_r would never find an 'ideal' host for which to
clear callbacks, since lih0_r and lih1_r required a non-NULL rock to do
anything. Remove the requirement for the passed-in host rock to be
non-NULL, and make lih*_r more threadsafe, by passing in a parameter
struct for the rock.

Also attempt to make the GSS_r code a bit more clear with some
descriptive variable names and such.

FIXES 126451

Reviewed-on: http://gerrit.openafs.org/1317
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit eb7d90fd0db68ea49ec1820adda599b5922c7de2)

Change-Id: I1c283153977f47cb21c57bf6e65305068c6fd3be
Reviewed-on: http://gerrit.openafs.org/1370
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit f3899ac3b342ad065dd9484720a4d721a3fb549a)