Set LDAP certificate trust options for LDAPS and TLS

We currently only set the LDAP library certificate trust options
when TLS is being used (via startTLS).  If regular LDAPS is being
used, the certificate trust options that are defined in Keystone's
configuration file are never actually set.

This patch sets the certificate trust options for both LDAPS and
TLS cases.

Conflicts:
        keystone/common/ldap/core.py
        keystone/tests/unit/common/test_ldap.py

Closes-bug: #1209343
Change-Id: Ieb94b732f623695920feb34995bb863175ddf27a
(cherry picked from commit ca50b6315909faf92db9eaf2981782bcd80cfab8)
Merge "Set LDAP certificate trust options for LDAPS and TLS" into stable/icehouse