Do not assume that every f29-gcc job produces coverage.xml

Change-Id: Icbde64c8654109ba93a49ccd293a1f60f0da7f22
diff --git a/zuul.yaml b/zuul.yaml
index c4b6a8d..dfe4c6e 100644
--- a/zuul.yaml
+++ b/zuul.yaml
@@ -27,16 +27,23 @@
     description: |
       Build on Fedora 29 with GCC.
     parent: run-ci-build-sh
-    post-run: playbooks/coverage-diff/upload.yaml
     vars:
       perform_extra_work: true
+
+- job:
+    name: f29-gcc-cover
+    description: |
+      Build on Fedora 29 with GCC.
+    parent: f29-gcc
+    post-run: playbooks/coverage-diff/upload.yaml
+    vars:
       coverage_xml_dir: "{{ ansible_user_dir }}/build"
 
 - job:
     name: f29-gcc-cover-diff
     description: |
       Compare difference in coverage as introduced by this change.
-    parent: run-ci-build-sh
+    parent: f29-gcc
     pre-run: playbooks/checkout-original-state/run.yaml
     run:
       - playbooks/run-test-command/run.yaml