Fix verification logic so we find all errors and report them at once

Currently, the drupalorg_drush plugin is littered with this construct:

        foreach ($info['libraries'] as $library => $library_data) {
          $pass = $pass && $library_transformer->verify($library_data, $library);
          $info['libraries'][$library] = $library_data;
        }
...

Due to short-circuit evaluation, as soon as we hit one verification failure, $pass will be FALSE and we'll never verify any other libraries in the make file. IMHO it's better to loop through everything so we can provide complete info to the end user about anything in their .make file that's not kosher, instead of just bailing out at the first error and only telling them about that.

Splitting this off from #684788-31: Verify Library URLs against a White-list for drupal-org.make point B, since it's not just about library verification, and it'll be cleaner to fix this in a separate commit so as not to confuse things...