project-config-grafyaml: pass source to tox

This job wants to run grafyaml from master (which is what happens on
the grafana server, as it installs from current git).  Pass the
grafyaml checkout so it can do this.

Change-Id: I57211ba4041bd567ad9e3134382c0ebd353da267
Needed-By: https://review.openstack.org/572083

zuul.d/jobs.yaml

@@ -996,13 +996,14 @@
       env.
     vars:
       tox_envlist: grafyaml
+      tox_environment:
+        GRAFYAML_SRC: "{{ ansible_user_dir }}/{{ zuul.projects['git.openstack.org/openstack-infra/grafyaml'].src_dir }}"
     required-projects:
       - openstack-infra/grafyaml
     files:
       - ^grafana/.*$
       - bindep.txt
       - other-requirements.txt
-      - tools/grafyaml-validate.sh
       - tox.ini
 
 - job: