Add migration tool for v2 to v3 conversion

We need to be able to generate a new v3 config based on our old v2
config. It won't be perfect, but should ultimately be no worse than the
v2.5 auto-generated playbooks.

Change-Id: I9cb676ceff01bbdb845d22774edbaa718323db27
diff --git a/setup.cfg b/setup.cfg
index ce7a40e..63ff562 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -27,6 +27,7 @@
     zuul-executor = zuul.cmd.executor:main
     zuul-bwrap = zuul.driver.bubblewrap:main
     zuul-web = zuul.cmd.web:main
+    zuul-migrate = zuul.cmd.migrate:main
 
 [build_sphinx]
 source-dir = doc/source
@@ -37,3 +38,5 @@
 [extras]
 mysql_reporter=
     PyMySQL
+migrate=
+    jenkins-job-builder==1.6.2