Reduce invasiveness of `bin/auth ldap`

Summary: The once-choppy LDAP waters seem to have calmed down a bit. Use the service profile log to get a pretty good idea of what's going on with LDAP (see D6391) instead of invasive logging to get a slightly better idea.

Test Plan:
  $ ~/src/php-src/sapi/cli/php -f ./bin/auth ldap --trace
  >>> [2] <connect> phabricator2_auth
  <<< [2] <connect> 1,755 us
  >>> [3] <query> SELECT * FROM `auth_providerconfig`  ORDER BY id DESC
  <<< [3] <query> 423 us
  Enter LDAP Credentials

      LDAP Username:  ldapuser
  >>> [4] <exec> $ stty -echo
  <<< [4] <exec> 10,370 us

      LDAP Password:  >>> [5] <exec> $ stty echo
  <<< [5] <exec> 6,844 us

  Connecting to LDAP...
  >>> [6] <ldap> connect (127.0.0.1:389)
  <<< [6] <ldap> 12,932 us
  >>> [7] <ldap> bind (sn=ldapuser,ou=People, dc=aphront, dc=com)
  <<< [7] <ldap> 6,860 us
  >>> [8] <ldap> search (ou=People, dc=aphront, dc=com, sn=ldapuser)
  <<< [8] <ldap> 5,907 us
  Found LDAP Account: ldapuser

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6392