xmlrpctests: remove harcoded expiration date from test_user_plugin
The test test_user_plugin is using a hardcoded date for
password expiration and started failed since we passed this date.
Replace the hardcoded date with now + 1 year.
Signed-off-by: Florence Blanc-Renaud <email@example.com>
Reviewed-By: Alexander Bokovoy <firstname.lastname@example.org>
Reviewed-By: Stanislav Levin <email@example.com>