Follow symlinks in the lookup

When the user gives a folder to the lookup, it's expected to work,
whatever the content of the folder is.

In the Zuul v3 case, we are symlinking the role that are checked
out as part of the Zuul dependency resolution, for example when
Depends-On is used.

If we don't follow symlinks, those checkout roles aren't part
of the repo build process, and won't be build.

Change-Id: Ic09f6a9ee28e3f7919226f22b803ee1a1b8ad53d

lookup/py_pkgs.py

@@ -346,7 +346,7 @@ class DependencyFileProcessor(object):
         :type path: ``str``
         :returns: ``list``
         """
-        paths = os.walk(os.path.abspath(path))
+        paths = os.walk(os.path.abspath(path), followlinks=True)
         files = list()
         for fpath, _, afiles in paths:
             for afile in afiles: