Bug 1840: 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 1840

Change-Id: I2cf79d9e697ba1267e2a8d00a180412a2887e1bd
Signed-off-by: beierlm <mark.beierl@canonical.com>
diff --git a/requirements.txt b/requirements.txt
index 2ca19f5..5d297e0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,15 +1,3 @@
-aiokafka==0.7.0
-    # via -r requirements.in
-dataclasses==0.6
-    # via -r requirements.in
-kafka-python==2.0.2
-    # via aiokafka
-pycrypto==2.6.1
-    # via -r requirements.in
-pymongo==3.11.3
-    # via -r requirements.in
-pyyaml==5.4.1
-    # via -r requirements.in
 #######################################################################################
 # Copyright ETSI Contributors and Others.
 #
@@ -26,3 +14,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #######################################################################################
+aiokafka==0.7.2
+    # via -r requirements.in
+dataclasses==0.6
+    # via -r requirements.in
+kafka-python==2.0.2
+    # via aiokafka
+pycrypto==2.6.1
+    # via -r requirements.in
+pymongo==3.12.3
+    # via -r requirements.in
+pyyaml==5.4.1
+    # via -r requirements.in