Filter lxc_images list per host

To greatly reduce the amount of log noise from skipped tasks, when
setting the 'lxc_images' var filter it to only include items that begin
with the 'cache_index_item' var. The when clauses in tasks that looped
through 'lxc_images' looking for this same match can be removed.

Change-Id: I4bf7b32faa9ed0a8cddeb0792f912c0100dbece8

tasks/lxc_cache_create.yml

@@ -40,8 +40,6 @@
     url: "{{ lxc_image_cache_server }}/{{ item.split(';')[-1] }}/meta.tar.xz"
     dest: "/tmp/meta.tar.xz"
   with_items: "{{ lxc_images }}"
-  when:
-    - item | match("^{{ cache_index_item }}")
 
 - name: Place container metadata
   unarchive:

tasks/lxc_cache_preparation.yml

@@ -26,7 +26,14 @@
 
 - name: Set image index fact
   set_fact:
-    lxc_images: "{{ image_index.content.splitlines() }}"
+    lxc_images: >
+      {%- set images = [] %}
+      {%- for image in image_index.content.splitlines() %}
+      {%- if image | match("^" + cache_index_item) %}
+      {%- set _ = images.append(image) %}
+      {%- endif %}
+      {%- endfor %}
+      {{- images -}}
 
 - include: "lxc_cache_preparation_systemd_{{ (systemd_version.stdout_lines[0].split()[-1] | int > 219) | ternary('new', 'old') }}.yml"
 

tasks/lxc_cache_preparation_systemd_new.yml

@@ -39,5 +39,3 @@
     - pull_image.rc != 0
     - "'failed' in pull_image.stderr | lower"
   with_items: "{{ lxc_images }}"
-  when:
-    - item | match("^{{ cache_index_item }}")

tasks/lxc_cache_preparation_systemd_old.yml

@@ -126,8 +126,6 @@
   retries: 3
   delay: 1
   with_items: "{{ lxc_images }}"
-  when:
-    - item | match("^{{ cache_index_item }}")
 
 - name: Place container rootfs
   unarchive: