parallel_emerge: update db api usage

The match_pkgs helper used to autoconvert the argument to an Atom
object if we passed in a string, but newer versions of portage no
longer do that.  Instead, the cp_list helper is meant for that, so
switch the call over to work with both versions.

BUG=chromium:462099
TEST=build works w/newer and older portage

Change-Id: If803466a7cbaa7e8ed03f6d2f06643b4f41424ff
Reviewed-on: https://chromium-review.googlesource.com/852915
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
diff --git a/scripts/parallel_emerge.py b/scripts/parallel_emerge.py
index fb9e893..d4e7d5a 100644
--- a/scripts/parallel_emerge.py
+++ b/scripts/parallel_emerge.py
@@ -1926,7 +1926,7 @@
   # pylint: disable=W0212
   if root == "/":
     final_db = emerge.depgraph._dynamic_config._filtered_trees[root]['graph_db']
-    for db_pkg in final_db.match_pkgs("sys-apps/portage"):
+    for db_pkg in final_db.cp_list("sys-apps/portage"):
       portage_pkg = deps_graph.get(db_pkg.cpv)
       if portage_pkg:
         portage_upgrade = True