Fix undefined matrix_postgres_backup_detected_version_corresponding_docker_image

.. and prevent variable name overlap with `matrix-postgres` for the
other variables as well.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/868

roles/matrix-postgres-backup/tasks/util/detect_existing_postgres_version.yml

@@ -5,52 +5,52 @@
 
 - name: Initialize Postgres version determination variables (default to empty)
   set_fact:
-    matrix_postgres_detection_pg_version_path: "{{ matrix_postgres_data_path }}/PG_VERSION"
-    matrix_postgres_detected_existing: false
-    matrix_postgres_detected_version: ""
-    matrix_postgres_detected_version_corresponding_docker_image: ""
+    matrix_postgres_backup_detection_pg_version_path: "{{ matrix_postgres_data_path }}/PG_VERSION"
+    matrix_postgres_backup_detected_existing: false
+    matrix_postgres_backup_detected_version: ""
+    matrix_postgres_backup_detected_version_corresponding_docker_image: ""
 
 - name: Determine existing Postgres version (check PG_VERSION file)
   stat:
-    path: "{{ matrix_postgres_detection_pg_version_path }}"
+    path: "{{ matrix_postgres_backup_detection_pg_version_path }}"
   register: result_pg_version_stat
 
 - set_fact:
-    matrix_postgres_detected_existing: true
+    matrix_postgres_backup_detected_existing: true
   when: "result_pg_version_stat.stat.exists"
 
 - name: Determine existing Postgres version (read PG_VERSION file)
   slurp:
-    src: "{{ matrix_postgres_detection_pg_version_path }}"
+    src: "{{ matrix_postgres_backup_detection_pg_version_path }}"
   register: result_pg_version
-  when: matrix_postgres_detected_existing|bool
+  when: matrix_postgres_backup_detected_existing|bool
 
 - name: Determine existing Postgres version (make sense of PG_VERSION file)
   set_fact:
-    matrix_postgres_detected_version: "{{ result_pg_version['content']|b64decode|replace('\n', '') }}"
-  when: matrix_postgres_detected_existing|bool
+    matrix_postgres_backup_detected_version: "{{ result_pg_version['content']|b64decode|replace('\n', '') }}"
+  when: matrix_postgres_backup_detected_existing|bool
 
 - name: Determine corresponding Docker image to detected version (assume default of latest)
   set_fact:
     matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_latest }}"
-  when: "matrix_postgres_detected_version != ''"
+  when: "matrix_postgres_backup_detected_version != ''"
 
 - name: Determine corresponding Docker image to detected version (use 9.x, if detected)
   set_fact:
     matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v9 }}"
-  when: "matrix_postgres_detected_version.startswith('9.')"
+  when: "matrix_postgres_backup_detected_version.startswith('9.')"
 
 - name: Determine corresponding Docker image to detected version (use 10.x, if detected)
   set_fact:
     matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v10 }}"
-  when: "matrix_postgres_detected_version == '10' or matrix_postgres_detected_version.startswith('10.')"
+  when: "matrix_postgres_backup_detected_version == '10' or matrix_postgres_backup_detected_version.startswith('10.')"
 
 - name: Determine corresponding Docker image to detected version (use 11.x, if detected)
   set_fact:
     matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v11 }}"
-  when: "matrix_postgres_detected_version == '11' or matrix_postgres_detected_version.startswith('11.')"
+  when: "matrix_postgres_backup_detected_version == '11' or matrix_postgres_backup_detected_version.startswith('11.')"
 
 - name: Determine corresponding Docker image to detected version (use 12.x, if detected)
   set_fact:
     matrix_postgres_backup_detected_version_corresponding_docker_image: "{{ matrix_postgres_backup_docker_image_v12 }}"
-  when: "matrix_postgres_detected_version == '12' or matrix_postgres_detected_version.startswith('12.')"
+  when: "matrix_postgres_backup_detected_version == '12' or matrix_postgres_backup_detected_version.startswith('12.')"