Change default for forcelegacy option

  - The default for forcelegacy is set to
    no, so the boolean of false is used to
    reflect that state.  Remove the previous
    default of undef.
  - Update the README to include the default
    in the example section.
  - Adjust order in which forcelegacy is displayed
    within the README example and within the parameters
    of the class.  Order change as a result of the
    configuration relationship between SSSD and forcelegacy.