The gPlazma cache used by NFS and SRM caches both positive and negative
replies. Unfortunately it also caches failures to communicate with gPlazma.
This means that a transient timeout would be cached too, thus increasing the
effect of the transient error.

This patch resolves this problem by not caching timeouts (which include failure
to communicate with gPlazma).

Other errors are still cached - the correctness of this is debatable when
gPlazma does not distinguish between transient and permanent errors.

Target: trunk
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Require-notes: yes
Require-book: no
Committed: 43ecb8c5ffac90014cf339560ca8f4640584c4bd
Acked-by: Albert Rossi <arossi@fnal.gov>
Patch: https://rb.dcache.org/r/7332
(cherry picked from commit 6bfdfa83d5b51c8601bd30d5de262ae032b14da8)

Conflicts:
	modules/dcache/src/main/java/org/dcache/services/login/CachingLoginStrategy.java
Merge pull request #860 from gbehrmann/fix/2.8/rb7332

The gPlazma cache used by NFS and SRM caches both positive and negative replies. Unfortunately it also caches failures to communicate with gPlazma. This means that a transient timeout would be cached too, thus increasing the effect of the transient error.