Make the LDAP debug option a configurable setting

The LDAP OPT_DEBUG_LEVEL is very useful for debugging LDAP
problems with Keystone. This change makes it easier to set
and find. The default will be to have it disabled.

DocImpact

Change-Id: I342fe2eea752bd8632074600386f0173e7328132
Merge "Make the LDAP debug option a configurable setting"