Add healthcheck plugin to the checks pipeline

Change-Id: I683c92c8fe8aebaec475afa5716e991d1882d335

zuul.d/projects.yaml

diff --git a/zuul.d/projects.yaml b/zuul.d/projects.yaml
index a858582..b129200 100644
--- a/zuul.d/projects.yaml
+++ b/zuul.d/projects.yaml
@@ -141,6 +141,12 @@
         - gerrit-plugin-build
 
 - project:
+    name: plugins/healthcheck
+    check:
+      jobs:
+        - gerrit-plugin-build
+
+- project:
     name: plugins/heartbeat
     check:
       jobs: