[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: #40230

Closes-Bug: #1886298

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

Change-Id: Icb075570aa1a8da7f8eed683b63c4f6df202486a

lower-constraints.txt

@@ -5,7 +5,7 @@ Babel==2.5.3
 bandit==1.4.0
 cachetools==2.0.0
 certifi==2018.1.18
-cffi==1.11.5
+cffi==1.14.0
 chardet==3.0.4
 cliff==2.11.0
 cmd2==0.8.2
@@ -29,7 +29,7 @@ future==0.16.0
 futurist==1.2.0
 gitdb==0.6.4
 GitPython==1.0.1
-greenlet==0.4.10
+greenlet==0.4.15
 idna==2.6
 iso8601==0.1.12
 Jinja2==2.10
@@ -40,7 +40,7 @@ jsonschema==2.6.0
 keystoneauth1==3.4.0
 kombu==4.0.0
 linecache2==1.0.0
-MarkupSafe==1.0
+MarkupSafe==1.1.1
 monotonic==1.4
 mox3==0.20.0
 msgpack==0.5.6
@@ -89,7 +89,7 @@ python-novaclient==10.1.0
 python-openstackclient==3.12.0
 python-subunit==1.0.0
 pytz==2018.3
-PyYAML==3.12
+PyYAML==3.13
 repoze.lru==0.7
 requests==2.18.4
 requestsexceptions==1.4.0

requirements.txt

@@ -12,4 +12,4 @@ oslo.log>=3.36.0 # Apache-2.0
 oslo.utils>=3.33.0 # Apache-2.0
 websocket-client>=0.44.0 # LGPLv2+
 docker>=2.4.2 # Apache-2.0
-PyYAML>=3.12 # MIT
+PyYAML>=3.13 # MIT