[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.

- Move multinode jobs to focal nodeset

Story: #2007865
Task: #40227

Closes-Bug: #1886298

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

Depends-On: https://review.opendev.org/#/c/752294/

Change-Id: Iec953f3294087cd0b628b701ad3d684cea61c057

requirements.txt

@@ -7,14 +7,14 @@ jsonpatch>=1.21 # BSD
 keystoneauth1>=3.4.0 # Apache-2.0
 jsonschema>=3.2.0 # MIT
 keystonemiddleware>=4.21.0 # Apache-2.0
-lxml>=4.1.1 # BSD
+lxml>=4.5.1 # BSD
 croniter>=0.3.20 # MIT License
 os-resource-classes>=0.4.0
 oslo.concurrency>=3.26.0 # Apache-2.0
 oslo.cache>=1.29.0 # Apache-2.0
 oslo.config>=5.2.0 # Apache-2.0
 oslo.context>=2.21.0 # Apache-2.0
-oslo.db>=4.35.0 # Apache-2.0
+oslo.db>=4.44.0 # Apache-2.0
 oslo.i18n>=3.20.0 # Apache-2.0
 oslo.log>=3.37.0 # Apache-2.0
 oslo.messaging>=8.1.2 # Apache-2.0
@@ -41,9 +41,9 @@ python-openstackclient>=3.14.0 # Apache-2.0
 python-ironicclient>=2.5.0 # Apache-2.0
 SQLAlchemy>=1.2.5 # MIT
 stevedore>=1.28.0 # Apache-2.0
-taskflow>=3.7.1 # Apache-2.0
+taskflow>=3.8.0 # Apache-2.0
 WebOb>=1.8.5 # MIT
 WSME>=0.9.2 # MIT
-networkx>=2.2 # BSD
+networkx>=2.4 # BSD
 microversion_parse>=0.2.1 # Apache-2.0
 futurist>=1.8.0 # Apache-2.0