(maint) Add -l to the wget call in retrieve

Now that we are retrieving more than just artifacts, wget needs to
recurse further than before. -r defaults to 5, which is insufficient for
our needs beyond artifacts. This commit updates adds `-l 0` to the wget
to trigger infinite recursion.
(maint) Add comments to the wget call in pl:jenkins:retrieve
Merge pull request #326 from haus/maint/master/add_more_wget_recursion

(maint) Add -l to the wget call in retrieve