Bug 1843: LTS Support

Updates base to Ubuntu 20.04
Updates python to 3.8
Updates pip dependencies to more recent versions
Adds apt cache to stage 2 dockerfile

Fixes bug 1843

Change-Id: Iec7c73cb99f5ed3f0e07666d8c8c8be8ca91c0ea
Signed-off-by: beierlm <mark.beierl@canonical.com>
diff --git a/requirements-dist.in b/requirements-dist.in
index 2b3c735..4f8784f 100644
--- a/requirements-dist.in
+++ b/requirements-dist.in
@@ -1,16 +1,18 @@
-# Copyright 2021 Canonical Ltd.
+# Copyright ETSI Contributors and Others.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
-#     http://www.apache.org/licenses/LICENSE-2.0
+#    http://www.apache.org/licenses/LICENSE-2.0
 #
-#     Unless required by applicable law or agreed to in writing, software
-#     distributed under the License is distributed on an "AS IS" BASIS,
-#     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-#     See the License for the specific language governing permissions and
-#     limitations under the License.
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
 
 stdeb
 setuptools-version-command
+setuptools<60
\ No newline at end of file