gplazma: make plugin creation caching optional

This patch introduces the gplazma.enable.plugin-creation-caching configuration property that
allows the admin to switch off the plugin cache.  This is useful as the cache is arguable a
misfeature and, in its current form, can lead to undesirable behaviour.

A subsequent patch (targeted at master only) will remove this feature.

Target: master
Patch: https://rb.dcache.org/r/7210/
Acked-by: Tigran Mkrtchyan
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Require-notes: true
Require-book: no
acl: add heuristic to detect acl format

there are two ways to define acl:

USER:7:rlwfx:o:ALLOW:FFFF
and
USER:7:i+rlwfx:o:FFFF

make ACE#parse() smart enouth to detect that.

Ticket: #8424
Acked-by: Karsten Schwank
Target: master, 2.10
Require-book: no
Require-notes: no