Avoid using released hosts

Avoid using released hosts

Since h_Release_r has the possibility of freeing a host, we should not
be using a host after it has been released. A few places can still use a
released host, potentially causing heap corruption, double frees, and
generally weird behavior.

So either move calls of h_Release_r until after we finish using a host,
or make sure to set the pointer to NULL after it has been released.

Change-Id: I3d5275c3862003e372d3c19a5462e62bf9cb269e
Reviewed-on: http://gerrit.openafs.org/747
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Dan Hyde <drh@umich.edu>
Reviewed-by: Derrick Brashear <shadow@dementia.org>