Wait for aria2c to finish

We launch aria2c in async without wait and hope that it will finish
in time before we start unarchive. However it's worth checking that
image download has really finished instead of making such assumption.

Additionally ensure that ubuntu has gzip installed, as their image is
gunzip compressed.

Change-Id: I1d7dc2ff6bc1fef6d1d2e5e56b10012c7d575f5e
Closes-Bug: 1895518

tasks/lxc_cache_preparation_simple.yml

@@ -64,6 +64,14 @@
     state: directory
   register: create_new_dir
 
+- name: Wait for base image download
+  async_status:
+    jid: "{{ prestage_image.ansible_job_id }}"
+  register: _lxc_prestage_image_result
+  until: _lxc_prestage_image_result.finished
+  delay: 5
+  retries: "{{ lxc_cache_prep_timeout | int // 5 }}"
+
 - name: Unpack base image
   unarchive:
     src: "/tmp/{{ cache_basename }}"

vars/ubuntu-18.04-host.yml

@@ -29,6 +29,7 @@ _lxc_hosts_distro_packages:
   - debootstrap
   - dnsmasq-base
   - git
+  - gzip
   - ifupdown
   - iptables
   - irqbalance

vars/ubuntu-20.04-host.yml

@@ -29,6 +29,7 @@ _lxc_hosts_distro_packages:
   - debootstrap
   - dnsmasq-base
   - git
+  - gzip
   - ifupdown
   - iptables
   - irqbalance