vos: refactor ListAddrs

vos: refactor ListAddrs

refactor ListAddrs to be more readable.   Clarify that -uuid and
-host cannot be issued at the same time.  Rename 'nentries' to
'max_index' so it is clear that ubik_VL_GetAddrs() is issued
to set an upper-bound for the number of subsequent ubik_VL_GetAddrsU()
calls that are issued when neither -host nor -uuid are specified.

Change-Id: Icbd511722728396fda837abba39a3e6809f4d26c
Reviewed-on: http://gerrit.openafs.org/4754
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>