[SSSD] [sssd PR#66][opened] Minor Dynamic DNS fixes

[fidencio]

   URL: https://github.com/SSSD/sssd/pull/66
Author: justin-stephenson
 Title: #66: Minor Dynamic DNS fixes
Action: opened

PR body:
"""
To provide a bit more information, one of the fixes is to correct NULL being printed
here(https://fedorahosted.org/sssd/ticket/3220):

   [nsupdate_msg_create_common] (0x0200): Creating update message for realm [(null)].

For the other(https://bugzilla.redhat.com/show_bug.cgi?id=1386748), It is not uncommon for
nsupdate to successfully update DNS records but report the error below which results in
return(2) to be called inside nsupdate code

    TSIG error with server: tsig verify failure

It is easy to reproduce with AD DNS changing Dynamic DNS to 'Nonsecure and secure'
on the Zone Properties.

This patch allows PTR records to continue when this happens, however in this case our
debug log messages still report failure and I think some improvement should be made
here(not sure how exactly though)

    [child_sig_handler] (0x1000): Waiting for child [3710].
    [nsupdate_child_handler] (0x0040): Dynamic DNS child failed with status [512]
    [child_sig_handler] (0x0020): child [3710] failed with status [2].
    [be_nsupdate_done] (0x0040): nsupdate child execution failed [1432158238]: Dynamic DNS
update failed

It would be nice to correct this at the nsupdate level if this is not the expected
behavior also.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/66/head:pr66
git checkout pr66