cell: Declassify eval failure as a bug

Currently, this is claimed to be a bug:

[Gerds-MacBook-Pro.local] (System) admin > eval sdsd
There is a bug here, please report to support@dcache.org: (3) Eval Result : sdsd

After applying this patch, we get:

[Gerds-MacBook-Pro.local] (System) admin > eval sds
(3) Eval Result : sds

Target: trunk
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Require-notes: yes
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: https://rb.dcache.org/r/7353/
(cherry picked from commit a85817f89123d0b9ec18e805ef7ce6e9cd360631)