Sorted arguments to groupby in all_newest
Sorted arguments to groupby in all_newest

Fix PluginCollection.all_newest.
Current implementation causes that sometimes there are duplicated
Plugins (but with different versions). That means the list is
larger than expected what was causing random test failures:
TestPluginCollection.test_all_newest

Change-Id: Ief60a5e559cbbe6a1f0cc55a6809a8d273e169df
Closes-Bug: #1551726

stackforge/fuel-web,stackforge/fuel-web,stackforge/fuel-web