Use nslcd for LDAP authentication, RedHat support

    - Instead of libpam-ldap and libnss-ldap (legacy code), set up the well
      supported nss-pam-ldapd instead (libpam-ldapd and libnss-ldapd.)
    - Allow this to work on RedHat as well (tested on CentOS 6.4 and Amazon
      Linux 2013.9.)
    - Instead of clobbering 4 pam.d files create one that only creates
      entries for LDAP instead of jeopardizing potential user modifications
      to those files. The files are evaluated as a whole directory, and
      order does not matter.
    - Stop depending on nscd. Users can opt-in to nscd by including the
      recipe, preferably after this one has run.
    - Support node[:openldap][:cafile] in more places.

After code review here I will submit this as a pull request to opscode-cookbooks/openldap@master