[goal] Migrate testing to ubuntu focal

As per victoria cycle testing runtime and community goal[1]
we need to migrate upstream CI/CD to Ubuntu Focal(20.04).

Fixing:
- bug#1886298
Bump the lower constraints for required deps which added python3.8 support
in their later version.

Story: #2007865
Task: #40186

[1] https://governance.openstack.org/tc/goals/selected/victoria/migrate-ci-cd-jobs-to-ubuntu-focal>

Change-Id: I482ac98bc56f0e3cfb8b767f47649da11ed1afab

lower-constraints.txt

@@ -2,11 +2,11 @@ alabaster==0.7.10
 appdirs==1.3.0
 asn1crypto==0.23.0
 Babel==2.3.4
-cffi==1.7.0
+cffi==1.14.0
 cliff==2.8.0
 cmd2==0.8.0
 coverage==4.0
-cryptography==2.1
+cryptography==2.7
 debtcollector==1.2.0
 decorator==3.4.0
 deprecation==1.0
@@ -24,7 +24,7 @@ jsonpointer==1.13
 jsonschema==2.6.0
 keystoneauth1==3.4.0
 linecache2==1.0.0
-MarkupSafe==1.0
+MarkupSafe==1.1.1
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0
@@ -55,7 +55,7 @@ python-novaclient==9.1.0
 python-subunit==1.0.0
 python-swiftclient==3.2.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==3.13
 requests==2.18.0
 requestsexceptions==1.2.0
 simplejson==3.5.1

requirements.txt

@@ -4,7 +4,7 @@
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 Babel!=2.4.0,>=2.3.4 # BSD
 cliff!=2.9.0,>=2.8.0 # Apache-2.0
-PyYAML>=3.12 # MIT
+PyYAML>=3.13 # MIT
 python-dateutil>=2.5.3 # BSD
 six>=1.10.0 # MIT
 tosca-parser>=1.6.1 # Apache-2.0