Set default expiry date of 2y for new keys

GnuPG since version 2.1.17 (2016-12-20) creates new
keys with a default expiry date of 2 years. Kleopatra did
not because it used the batch gen key API.

This commit changes it so that default keys created by Kleopatra
match the default of GnuPG.

GnuPG-Bug-Id: T3229