bindep: skip package install when not needed

When bindep test doesn't output package, there is no need
to run the package task.

Change-Id: I6f13e060a6d9657d3dec4f43a0b9c2dbff2d362d

roles/bindep/tasks/packages.yaml

@@ -8,6 +8,7 @@
     name: "{{ bindep_output.stdout_lines }}"
     state: present
   become: yes
+  when: bindep_output.stdout_lines
 
 - name: Check that packages are installed
   command: "{{ bindep_run }}"