Fix bootstrap-servers on Ansible 2.6+

Recently as part of adding support for Docker CE we added the following
task to the baremetal role:

- name: Update yum cache
  yum:
    update_cache: yes
  become: True
  when: ansible_os_family == 'RedHat'

This works fine on Ansible 2.5, but no longer works on Ansible
2.6, which complains that either the 'name' or 'list' argument
is mandatory for the yum module.

This change updates the cache later on, when installing packages.

Change-Id: I1a158bda52c4e362cb12d361d7f961cfc699b385
Closes-Bug: #1819173

ansible/roles/baremetal/tasks/install.yml

@@ -5,12 +5,6 @@
   become: True
   when: ansible_os_family == 'Debian'
 
-- name: Update yum cache
-  yum:
-    update_cache: yes
-  become: True
-  when: ansible_os_family == 'RedHat'
-
 # TODO(inc0): Gates don't seem to have ufw executable, check for it instead of ignore errors
 - name: Set firewall default policy
   become: True
@@ -62,6 +56,7 @@
   package:
     name: "{{ item }}"
     state: present
+    update_cache: yes
   become: True
   with_items:
     - deltarpm
@@ -71,6 +66,7 @@
   package:
     name: "{{ item }}"
     state: present
+    update_cache: yes
   become: True
   with_items: "{{ redhat_pkg_install }}"
   when: ansible_os_family == 'RedHat'