Update keyword to become instead of sudo

Zuul updated ansible to 2.9 and broke one of the playbooks
that had the old sudo keyword, which is no longer valid in 2.9.

This change updates the offending file to use "become" instead,
which is the valid keyword instead of sudo.

Change-Id: I2057de7470d65a60c4c984cb99d0715c9d43b3a8

roles/upgrade-host/tasks/main.yaml

@@ -26,7 +26,7 @@
             - linux-generic-hwe-16.04
     - name: Reboot Host following kernel upgrade
       shell: sleep 2 && reboot
-      sudo: yes
+      become: yes
       async: 30
       poll: 0
       ignore_errors: true