common: Accept the Z-suffix for yymmddThhmmssZ format.
* common/gettime.c (isotime_p): Accept the Z suffix.
The intention is use for human interface.
(cherry picked from commit ba8afc4966cca1f6aaf9b2a9bfc3220782306c2b)
- GnuPG-bug-id: T3278
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>