moved LDAP sync to after initialization in User

Having the ldap sync code in the ‘before_create’ callback made the
validations unhappy, since validation happens before the create action.
Wrapped up the setting of a default role and syncing ldap attributes
into a User#setup_user_attributes method.

Also setup the “in_ldap” check to cache the results after making a
successful query, and return the cached value if available.  This
allows multiple queries to in_ldap? without hitting the LDAP server
each time