CVE-2020-25717 wb_sids2xids: build state->idmap_doms based on wb_parent_idmap_config

CVE-2020-25717 wb_sids2xids: build state->idmap_doms based on wb_parent_idmap_config

In future we'll try to avoid wb_lookupsids_send() and only call
it if needed.

The domain name passed should be only relevant to find the correct
idmap backend, and these should all be available in
wb_parent_idmap_config as it was created before the idmap child was forked.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14539

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14556

(cherry picked from commit c55f4f37589130a0d8952489da175bbcf53f6748)