Add support for protected jobs

For some use cases protected jobs can be useful. Protected jobs can
only be inherited by jobs defined in the same project. This adds
support for these protected jobs.

Change-Id: I62a8ecbbfa9eec54ab599bb34148976dcabfd40a
diff --git a/tests/fixtures/config/protected/main.yaml b/tests/fixtures/config/protected/main.yaml
new file mode 100644
index 0000000..5f57245
--- /dev/null
+++ b/tests/fixtures/config/protected/main.yaml
@@ -0,0 +1,9 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project
+          - org/project1