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