Update docker image

Switch to ubuntu:20.04 as a base image
to use python3.8 natively and to support the
latest CVE fixes for python packages

Related-Prod: PROD-36143
Change-Id: I5e1e8fb6d3b4987522a96b621898afd08958fe20
diff --git a/test_set/cvp-spt/requirements.txt b/test_set/cvp-spt/requirements.txt
index 294aece..6898f80 100644
--- a/test_set/cvp-spt/requirements.txt
+++ b/test_set/cvp-spt/requirements.txt
@@ -5,6 +5,6 @@
 python-keystoneclient==3.22.0  # Apache-2.0
 python-neutronclient==7.1.0 # Apache-2.0
 python-novaclient==7.1.0
-PyYAML==5.3.1  # MIT
+PyYAML>=5.4  # MIT
 requests==2.24.0 # Apache-2.0
-texttable==1.2.0
\ No newline at end of file
+texttable==1.2.0