Bug 1689040 - bump update-verify docker image to ubuntu 20.04. r=bhearsum

Use python3 in more places so we don't have to explicitly install
the python 2.x package.

The newer version of curl in 20.04 will hopefully fix the intermittent
http2 framing errors we've been seeing recently.

Differential Revision: https://phabricator.services.mozilla.com/D106259

taskcluster/docker/update-verify/Dockerfile

@@ -1,6 +1,6 @@
 # This is an LTS! We should upgrade after the next LTS is released, unless
 # we've switched to the in-tree debian base images by then.
-FROM ubuntu:18.04
+FROM ubuntu:20.04
 
 MAINTAINER release@mozilla.com
 

taskcluster/docker/update-verify/system-setup.sh

@@ -13,8 +13,6 @@ apt_packages=()
 apt_packages+=('curl')
 apt_packages+=('locales')
 apt_packages+=('git')
-apt_packages+=('python')
-apt_packages+=('python-pip')
 apt_packages+=('python3')
 apt_packages+=('python3-pip')
 apt_packages+=('shellcheck')

tools/update-verify/release/compare-directories.py

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this file,
 # You can obtain one at http://mozilla.org/MPL/2.0/.

tools/update-verify/release/updates/verify.sh

@@ -229,7 +229,7 @@ do
                 echo "Unknown override cert - skipping"
                 ;;
             esac
-            python "${cert_replacer}" "${MY_DIR}/../mar_certs" "${updater}.orig" "${updater}" ${overrides}
+            python3 "${cert_replacer}" "${MY_DIR}/../mar_certs" "${updater}.orig" "${updater}" ${overrides}
         else
             echo "override_certs is '${override_certs}', not replacing any certificates"
         fi

tools/update-verify/scripts/chunked-verify.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this file,
 # You can obtain one at http://mozilla.org/MPL/2.0/.