chore(docs build): add flag to control log output level

closes #1823

Gulp targets like `check-deploy` and `serve-and-sync-devguide` are
quite verbose. This PR allows the `dgeni` logging level to be
controlled using the `--dgeni-log` flag. E.g., use `--dgen-log="error"`
to see only errors.

Also sets log level to "error" when gulp is silent
and log level for createShredMapPackage

tools/api-builder/docs-package/index.js

@@ -20,11 +20,6 @@ module.exports = new Package('angular-v2-docs', [jsdocPackage, nunjucksPackage,
 .processor(require('./processors/addNotYetDocumentedProperty'))
 .processor(require('./processors/createDecoratorDocs'))
 
-// Configure the log service
-.config(function(log) {
-  log.level = 'info';
-})
-
 .config(function(parseTagsProcessor) {
   parseTagsProcessor.tagDefinitions.push({ name: 'internal', transforms: function() { return true; } });
   parseTagsProcessor.tagDefinitions.push({ name: 'syntax' });