Remove log entries containing user name from authenticator (#199)

* Update authenticator classes to remove logging of user.

* Bump version number to 2.0.16

v2.2.1 includes minor fixes

* inline files.write() in GenApiConfigAction
* improve Swagger generation
* convert standard logging to use flogger

v2.2.0 includes some major functionality changes

* improved OAuth2 scope handling
* some refactors to allow advanced users to extend/override default
  Endpoints behavior (auth code, serialization)
* greatly improved resource usage by serializing the response object
  to stream instead of storing the whole result in memory first
* improved OpenAPI compatibility
* google-http-client is bumped to 1.25.0 to address vulnerabilities
* deprecate JsonMap schema generation in favor of using
  additionalProperties, the standard for JSON schema. This feature can
  be turned off by setting environment variable
  ENDPOINTS_MAP_FORCE_JSON_MAP_SCHEMA to true, or by setting the
  system property endpoints.mapSchema.forceJsonMapSchema to true. This
  new functionality can be further configured (see
  EndpointsFlag.java).
* add option to disable Jackson annotation integration. Set
  environment variable ENDPOINTS_JSON_USE_JACKSON_ANNOTATIONS to false
  or system property endpoints.json.useJacksonAnnotations to false.
* support multipart/form-data requests for requests that are all named
  parameters

v2.1.2 fixes a few issues

* print full exception info on tool failure
* OpenAPI spec generation now checks that -o argument isn't a
  directory
* update Jackson dependency to 2.9.6 to address CVE-2017-7525

v2.1.1 fixes two minor issues

* OpenAPI spec generation now sets a string type for enums
* a printStackTrace() call has been changed to use a java.util logger

v2.1.0 fixes some compatibility issues

* underscores are allowed in API names in very old versions of Endpoints
  v1, so we allow them without adding them to the documentation.
* required parameters now have null checking added to them.

v2.0.14 includes minor fixes and features

* re-add canonical name to discovery generation
* add description for enum constants used in parameters
* add retry logic for getting token info
* don't generate web accessible discovery for APIs that have
  discoverable set to false

v2.0.13 fixes list path parameter deserialization

v2.0.12 adds minor improvements and bug fixes

* discovery parameterOrder more closely matches original behavior
* discovery now has enum description support
* schema properties can be documented via @ApiResourceProperty
* API Explorer now uses the new Google icon
* null exception messages no longer cause a server error

v2.0.11 updates dependency versions

Most notably, the API client version has been changed to 1.23.0. This
is due to the fact that client libraries now generate with 1.23.0 as a
base, these clients are backwards incompatible.