Bug 1849: 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 1849

Change-Id: I8a589bbc76bb11f4bc0c42ebb727729da5c5c906
Signed-off-by: beierlm <mark.beierl@canonical.com>
diff --git a/tox.ini b/tox.ini
index 699ff96..c650490 100644
--- a/tox.ini
+++ b/tox.ini
@@ -199,15 +199,19 @@
 
 #######################################################################################
 [testenv:pip-compile]
-deps =  pip-tools==5.5.0
+deps =  pip-tools==6.4.0
 skip_install = true
-whitelist_externals = sh
+whitelist_externals = bash
+        [
 commands =
-        - sh -c "for file in requirements*.in ; do pip-compile -rU --no-header $file ;\
+        - bash -c "for file in requirements*.in ; do \
+        UNSAFE="" ; \
+        if [[ $file =~ 'dist' ]] ; then UNSAFE='--allow-unsafe' ; fi ; \
+        pip-compile -rU --no-header $UNSAFE $file ;\
         out=`echo $file | sed 's/.in/.txt/'` ; \
         sed -i -e '1 e head -16 tox.ini' $out ;\
         done"
-        - sh -c "sed -i 's/.*RO-plugin/-e RO-plugin/g' requirements-test.txt"
+        - bash -c "sed -i 's/.*RO-plugin/-e RO-plugin/g' requirements-test.txt"
 
 
 #######################################################################################