Make the test pass with GnuPG 2.3 and not too old 2.2.x

* Require at least GnuPG 2.2.2
* Use the compatibility helper for the test
* Support int and uint as type of ldaptimeout
* Change expected default of ldaptimeout to 15 (changed in GnuPG 2.2.2)
* Use gpgsm/keyserver instead of long gone dirmngr/LDAP Server

GnuPG-bug-id: 5217