'ansible_become' defined as a host_var or in the inventory for a host
has a higher precedence than 'become' defined within a playbook.

In change Id5b76a87809f03951c954fc3d752419a673403f7, 'become' was
defined explicitly for each play running against localhost so
'ansible_become' should be removed from its host_vars.

Change-Id: I0a3019ed7f4e151625682d009e5359378152592d