viced: Do not swallow errors on StoreData recovery

viced: Do not swallow errors on StoreData recovery

When we encounter any error in the StoreData fetch/store loop, we
reset the disk usage to ensure it remains correct, even in the face of
unexpected errors. However, when we do so, we use the errorCode from
VAdjustDiskUsage as our return value; if it is 0, we return success,
ignoring the error that got us in this code path in the first place.

Instead, keep track of a temporary errorCode for the disk usage
adjustment, and do not override our return value if there was no error
in the disk usage numbers.

Reviewed-on: http://gerrit.openafs.org/5645
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit dd831c09602f1ef16cc7dece84aeff638cce7272)

Change-Id: I154e6cbc96ee4e32bee2da77441547c1dce8b42c
Reviewed-on: http://gerrit.openafs.org/5711
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>