aklog: Clean up cell handling

aklog: Clean up cell handling

Clean up the aklog get_cellconfig routine, so that it is no longer
reliant upon global variables.
  * Tidy the handling of local_cell, and use dynamically allocated,
    rather than fixed length buffers.
  * Use the cell name contained within the afsconf_cell structure,
    rather than a local copy
  * Access linked cell information from afsconf_cell, rather than
    explicitly returning it
  * Don't use globals for linkedcell

Change-Id: I6ad42c70dcac7f285997be7c95a77dc67bf63679
Reviewed-on: http://gerrit.openafs.org/1321
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>