tools: Fix error if LDAP server cannot be resolved

Fixes error message in engine-manage-domains if LDAP server cannot be
resolved.

Change-Id: I8a234d08979b97d8695bb3b7afb76e6998b38c87
Bug-Url: https://bugzilla.redhat.com/1001976
Signed-off-by: Martin Perina <mperina@redhat.com>