core: enable resolver socket factory to accept plain address

this is disabled by default as it is a hack to overcome
unboundid-ldapsdk limitations, refer to README.unboundid-ldapsdk for
more information.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1134062
Change-Id: If7e82bfd024918525b1215d920f52b11f1f46804
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>