Fix: Document CL 4.X Ansible caveats, use Linux in tests

New versions of Ansible no longer work with Python release 3.7 running
on the managed nodes, affecting Cumulus Linux 4.x. The final fix has
already been implemented, this is a hotfix for release 1.9.2-post1 as
we're hitting this bug in the wild. It documents the caveat and uses
Linux as the device in the Libvirt and Virtualbox initial tests.

docs/caveats.md

@@ -187,6 +187,7 @@ ansible-galaxy collection install git+https://github.com/jmussmann/ansible_colle
 ## Cumulus Linux
 
 * The Cumulus VX 4.4.0 Vagrant box for VirtualBox is broken. *netlab* is using Cumulus VX 4.3.0 with *virtualbox* virtualization provider.
+* The Cumulus VX 4.x uses Python version 3.7, which recent versions of Ansible refuse to work with. The permanent fix is coming in release 1.9.3. Until then, use the **frrouting** device or [Cumulus VX 5.x image](caveats-cumulus-5x).
 
 _netlab_ uses the VLAN-aware bridge paradigm to configure VLANs on Cumulus Linux. That decision results in the following restrictions:
 
@@ -210,10 +211,11 @@ You could configure Cumulus Linux 5.x with configuration templates developed for
 
 NVUE has several shortcomings that prevent *netlab* from configuring basic designs like IBGP on top of IGP. Don't be surprised if the labs that work with **cumulus** device don't work with **cumulus_nvue** device, and please create a GitHub issue whenever you find a glitch. We'd love to know (at least) what doesn't work as expected.
 
+(caveats-cumulus-5x)=
 To run Cumulus Linux 5.x with **cumulus** device type, set the following default values in [lab topology](defaults-topology) or one of the [defaults files](defaults-user-file):
 
 ```
-defaults.devices.cumulus.libvirt.image: CumulusCommunity/cumulus-vx:5.2.0
+defaults.devices.cumulus.libvirt.image: CumulusCommunity/cumulus-vx:5.10.0
 defaults.devices.cumulus.libvirt.memory: 2048
 ```
 

netsim/templates/tests/libvirt.yml

@@ -3,10 +3,9 @@
 #
 ---
 defaults:
-  device: cumulus
+  device: linux
 
 provider: libvirt
 
-module: [ ospf ]
 nodes: [ s1, s2, s3 ]
-links: [ s1-s2, s2-s3, s1-s2-s3 ]
+links: [ s1-s2, s1-s2-s3 ]

netsim/templates/tests/virtualbox.yml

@@ -3,11 +3,9 @@
 #
 ---
 defaults:
-  device: cumulus
+  device: linux
 
 provider: virtualbox
 
-module: [ ospf ]
-
 nodes: [ s1, s2, s3 ]
-links: [ s1-s2, s2-s3, s1-s2-s3 ]
+links: [ s1-s2, s1-s2-s3 ]