[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: #40207

Closes-Bug: #1886298

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

Change-Id: I98cf0e5cee8f1996943b6274e914fcbca667fef7

lower-constraints.txt

@@ -11,13 +11,13 @@ extras==1.0.0
 fixtures==3.0.0
 gitdb==0.6.4
 GitPython==1.0.1
-greenlet==0.4.10
+greenlet==0.4.15
 imagesize==0.7.1
 iso8601==0.1.11
 Jinja2==2.10
 keystoneauth1==3.4.0
 linecache2==1.0.0
-MarkupSafe==1.0
+MarkupSafe==1.1.1
 mox3==0.20.0
 msgpack-python==0.4.0
 netaddr==0.7.18
@@ -35,7 +35,7 @@ pyparsing==2.1.0
 python-mimeparse==1.6.0
 python-subunit==1.0.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==3.13
 requests==2.14.2
 requestsexceptions==1.2.0
 rfc3986==0.3.1

test-requirements.txt

@@ -9,7 +9,7 @@ stestr>=2.0.0 # Apache-2.0
 # for testing optional parts
 oslo.config>=5.2.0 # Apache-2.0
 eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT
-greenlet>=0.4.10 # MIT
+greenlet>=0.4.15 # MIT
 
 coverage!=4.4,>=4.0 # Apache-2.0