openafs-client: cleanup PPA install

Over time we've had various different reasons for installing our own
OpenAFS packages in various situations and we haven't kept the when:
flags totally up to date.  Currently, we need the 1.8.6-5 packages
with the January 20201 timestamp fix installed everywhere; fix this.

I think that on long-running servers, the have the PPA installed from
prior iterations (I don't think we've ever *removed* it).  So things
like executors are still running with our packages, perhaps somewhat
unintentionally.

Update the comments a little to reflect what's going on.

Change-Id: I6a58c23daf85cf8fa005e3dad84a665343a947bc

roles/openafs-client/tasks/openafs-client/Debian.yaml

@@ -1,19 +1,21 @@
-# Bionic and Focal versions both shipped unstable ~pre versions of
+# OpenAFS distro packages have been a little inconsistent; for example
-# openafs clients; we thus have stable versions in a PPA.  We use this
+# Buster and Focal both shipped 1.8 "-pre" versions that upstream did
-# everywhere but our legacy Xenial x86 hosts (Debian stable has 1.8
+# not consdier ready for release.  There have been occasional bugs we
-# inbuilt so we are good there).
+# need fixed in production, and other things we've needed pulled in
-# https://bugs.launchpad.net/ubuntu/+source/openafs/+bug/1832690
+# like ARM64 support.  So that's why we maintain our own packages
+# here.
 - name: Install openstackci openafs PPA on Ubuntu
   apt_repository:
     repo: 'ppa:openstack-ci-core/openafs'
   when:
-    - ansible_distribution == 'Ubuntu' and not
+    - ansible_distribution == 'Ubuntu'
-      ( ansible_distribution_version is version('16.04', '==') and
-        ansible_architecture == 'x86_64' )
   become: yes
 
-# We install the ppa on debian too in order to get the fixed pacakages
+# 2021-01-20 : for now we install the ppa on debian too in order to
-# in our PPA
+# get the 1.8.6-5 era packages that fixed a timestamp rollover issue
+# (see 1.8.7 release notes).  This can likely be removed if backports
+# make it to stable; see
+# https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=980115
 - name: Install openstackci openafs PPA on Debian
   apt_repository:
     repo: 'ppa:openstack-ci-core/openafs'