Implement hashStream

Add a hashStream method to lib/hash that does the same as hashFile only
with a stream instead of a file path and implement tests for both of
these methods.

test/missing.js

@@ -4,7 +4,6 @@
 require('lib/clusterTools');
 require('lib/dole_nn_base');
 require('lib/getInstances');
-require('lib/hash');
 require('lib/manager/instanceManager');
 require('lib/manager/modManager');
 require('lib/manager/pluginManager');