Improve job dependencies using graph instead of tree

This replaces the job dependency tree with a graph so that we can
indicate that a job should wait until one or more jobs are complete
before starting.

Project pipeline job definitions are now a flat list, with each job
specifying its dependencies as the job attribute 'dependencies'.

Fixes bug #1166937.

Signed-off-by: Fredrik Medley <fredrik.medley@autoliv.com>
Signed-off-by: Fredrik Medley <fredrik.medley@gmail.com>
Signed-off-by: James E. Blair <jeblair@redhat.com>
Co-Authored-By: James E. Blair <jeblair@redhat.com>
Change-Id: I921940cafeea0738c39deb99357cfd7c91592359
diff --git a/tests/fixtures/config/dependency-graph/main.yaml b/tests/fixtures/config/dependency-graph/main.yaml
new file mode 100644
index 0000000..d9868fa
--- /dev/null
+++ b/tests/fixtures/config/dependency-graph/main.yaml
@@ -0,0 +1,8 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-repos:
+          - common-config
+        project-repos:
+          - org/project