Currently when validating the ansible installation, zuul only checks
if ansible is installed and not any packages that would have been
installed with ANSIBLE_EXTRA_PACKAGES. Since the executor image has
ansible pre installed the ANSIBLE_EXTRA_PACKAGES environment variable
has no effect unless ansible is removed.
This adds a check to make sure packages specified with
ANSIBLE_EXTRA_PACKAGES are installed as well.
Change-Id: I7ee4125d6716db718bb355b837e90dbcfce9b857