Use pcp instead of dstand and return dstat graph artifact

Dstat is dead, but pcp supplies a compatible interface.

Installation can be unreliable, so let's ignore failures since
this isn't generally critical.

Change-Id: I9234b226242f145db9c235797649202aa530ec74

roles/dstat-graph/tasks/main.yaml

@@ -18,3 +18,13 @@
   shell: "./generate_page.sh {{ dstat_data_path }} > {{ ansible_user_dir }}/zuul-output/logs/dstat.html"
   args:
     chdir: "{{ dstat_path }}"
+
+- name: Return dstat artifact to Zuul
+  zuul_return:
+    data:
+      zuul:
+        artifacts:
+          - name: "Dstat graph"
+            url: "dstat.html"
+            metadata:
+              type: dstat_graph

roles/run-dstat/tasks/main.yaml

@@ -1,9 +1,11 @@
 - name: Install dstat
   package:
-    name: dstat
+    name: pcp
     state: present
   become: true
+  failed_when: false
 - name: Run dstat
   shell: "dstat -tcmndrylpg --tcp --output {{ dstat_data_path }} >& /dev/null &"
   args:
     executable: /bin/bash
+  failed_when: false