copr: builders: don't require file edits to define prepare_base_image

From now on, it should be enough to run
$ ansible-playbook -e prepare_base_image=1 <the_spawning_playbook>

roles/copr/backend/files/provision/_provision_aarch64.yml

@@ -11,7 +11,6 @@
     - vars.yml
     - nova_cloud_vars.yml
   vars:
-    prepare_base_image: False
     ansible_python_interpreter: /usr/bin/python3
 
   tasks:

roles/copr/backend/files/provision/builderpb_nova.yml

@@ -43,8 +43,6 @@
     - nova_cloud_vars.yml
 
   vars:
-    # change this to True if you need to create new base image from snapshot
-    prepare_base_image: False
     ansible_python_interpreter: /usr/bin/python3
 
   tasks:

roles/copr/backend/files/provision/builderpb_nova_ppc64le.yml

@@ -43,8 +43,6 @@
     - nova_cloud_vars.yml
 
   vars:
-    # change this to True if you need to create new base image from snapshot
-    prepare_base_image: False
     ansible_python_interpreter: /usr/bin/python3
 
   tasks:

roles/copr/backend/files/provision/offloading_hack.yml

@@ -3,7 +3,7 @@
 
 - name: install ethtool
   package: state=present name=ethtool
-  when: prepare_base_image
+  when: prepare_base_image is defined
 
 - name: disable offloading
   command: ethtool -K eth0 tso off gro off gso off

roles/copr/backend/files/provision/provision_builder_tasks.yml

@@ -1,13 +1,13 @@
 - name: put infra repos into yum.repos.d
   copy: src=files/dnf/infra-tags.repo dest=/etc/yum.repos.d
   when:
-  - prepare_base_image
+  - prepare_base_image is defined
 
 - name: put infra stg repos into yum.repos.d if staging
   copy: src=files/dnf/infra-tags-stg.repo dest=/etc/yum.repos.d
   when:
     - devel
-    - not prepare_base_image
+    - not prepare_base_image is defined
 
 - name: disable updates-testing
   file:
@@ -15,7 +15,7 @@
     state: absent
 
 - shell: dnf -y upgrade
-  when: prepare_base_image
+  when: prepare_base_image is defined
 
 - name: set bigger timeout for yum
   ini_file: dest=/etc/yum.conf section=main option=timeout value=1000
@@ -29,7 +29,7 @@
     - "@copr/copr"
   when:
     - devel
-    - not prepare_base_image
+    - prepare_base_image is not defined
 
 - name: clean dnf cache
   shell: dnf clean all