I've tried to commenting out this line on /etc/pam.d/password-auth:
auth requisite pam_succeed_if.so uid >= 1000 quiet_success
However, although it has stopped complaining about "requirement uid >= 1000 not
met by user vdsm" on /var/log/secure , the error trying to attach ISO Domain to
Datacenter still persists, showing the same error message, so it looks that this was not
the cause of the problem :-(
Going back to stage zero.