gerrit: copy theme plugin from plugins/

This is a minor refactor to make a follow-on that copies static files
more logical.

Change-Id: Id31106a875926dd4eca31972b1fc52a1cd0b67bd

docker/gerrit/bazel/Dockerfile

@@ -21,5 +21,7 @@ COPY bazel-bin/release.war /var/gerrit/bin/gerrit.war
 RUN mkdir /var/gerrit/plugins && \
   unzip -jo /var/gerrit/bin/gerrit.war WEB-INF/plugins/* -d /var/gerrit/plugins
 
+# NOTE(ianw) : copied into build context by playbooks/zuul/gerrit/run.yaml
 COPY opendevtheme.html /var/gerrit/plugins/opendevtheme.html
+
 COPY bazel-bin/plugins/zuul-results-summary/zuul-results-summary.jar /var/gerrit/plugins/zuul-results-summary.jar

playbooks/zuul/gerrit/run.yaml

@@ -36,7 +36,7 @@
 
     - name: Install OpenDev theme plugin
       copy:
-        src: opendevtheme.html
+        src: plugins/opendevtheme.html
         dest: /home/zuul/src/gerrit.googlesource.com/gerrit/opendevtheme.html
 
     - name: Build docker image