swapon: use a loopback device

btrfs does not support swapfile. With a loopback device, we bypass the
limitation.

Also, ensure we've got the right Python 3.9 package installed.

tools/test-setup.sh

@@ -4,8 +4,9 @@ set -euxo pipefail
 
 sudo dd if=/dev/zero of=/swap.img bs=1024 count=1048576
 sudo chmod 600 /swap.img
-sudo mkswap /swap.img
-sudo swapon /swap.img
+sudo losetup -f /swap.img
+sudo mkswap $(sudo losetup --associated /swap.img|sed 's,:.*,,')
+sudo swapon $(sudo losetup --associated /swap.img|sed 's,:.*,,')
 
 # Platforms coverage:
 # Fedora 30 : has vagrant-libvirt no compilation needed

tools/tox-py39/pre.yml

@@ -1,8 +1,17 @@
 ---
 - hosts: all
   tasks:
-    - name: Ensure python3.9 is present
+    - name: Ensure python3.9 is present (Debian/Ubuntu)
       become: true
       package:
-        name: python
+        name: python3i9-devel
         state: present
+      when: ansible_os_family != "RedHat"
+    - name: Ensure python3.8 is present (Red Hat)
+      become: true
+      package:
+        name:
+          - python3.9
+          - gcc
+        state: present
+      when: ansible_os_family == "RedHat"