libafs: retry retriable RPCs instead of abandoning

libafs: retry retriable RPCs instead of abandoning

if we get e.g. an idle dead error we should retry
retriable actions, namely data stores. in order
for writing files to work correctly given how
the writeback code is structured it's important that
this not interfere with analyze's shouldRetry decision
on those RPCs

Reviewed-on: http://gerrit.openafs.org/6749
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 75a3dabe66a9fbc232b05e2f744ad5b867e18262)

Change-Id: I9c611eeb9a71298e9725268392cdf94074324bf1
Reviewed-on: http://gerrit.openafs.org/6777
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>