Bug 19625: Enable Shibboleth auto-provisioning for Plack

Bug 19625: Enable Shibboleth auto-provisioning for Plack

Test plan:
1. In $KOHA_CONF, check that //shibboleth/autocreate is set to 1
2. Find a user in Shibboleth that is not in Koha (or remove it from
   Koha)
3. Login with that user
4. Verify that the userid is not set correctly in Koha database
5. Apply the patch (restart starman)
6. Repeat steps 2 and 3
7. Verify that the userid is set correctly and the other
mapped fields if there are some

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>