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/requirements-dev.txt b/requirements-dev.txt
index 0359fb8..21f6ba6 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #######################################################################################
-aiokafka==0.7.0
+aiokafka==0.7.2
     # via -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
 dataclasses==0.6
     # via -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
@@ -22,11 +22,11 @@
     # via
     #   -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
     #   aiokafka
-git+https://osm.etsi.org/gerrit/osm/common.git@master#egg=osm-common
+osm-common @ git+https://osm.etsi.org/gerrit/osm/common.git@master
     # via -r requirements-dev.in
 pycrypto==2.6.1
     # via -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
-pymongo==3.11.3
+pymongo==3.12.3
     # via -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
 pyyaml==5.4.1
     # via -r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master