RUBY-577: temporarily disable testing on travis

The patch for enabling auth on Travis has not been pushed to the travis
workers yet:

travis-ci/travis-cookbooks#180

Once it has been rolled out we can remove the skipping of this test.

Author: TylerBrock

test/shared/authentication.rb

@@ -60,6 +60,10 @@ def test_authenticate_non_existent_user
   def test_delegated_authentication
     return if @client.server_version < '2.4'
 
+    # TODO: remove this line when slaves have this code:
+    # https://github.com/travis-ci/travis-cookbooks/pull/180
+    return if ENV['TRAVIS']
+
     doc = {'_id' => 'test'}
     # create accounts database to hold user credentials
     accounts = @client['accounts']