[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: #40190

Closes-Bug: #1886298

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

Change-Id: I602c3ce7c94a039e3fd550cbb47a8e8f095aacea

lower-constraints.txt

@@ -4,12 +4,12 @@ Babel==2.5.3
 bandit==1.1.0
 beautifulsoup4==4.6.0
 certifi==2018.1.18
-cffi==1.11.5
+cffi==1.14.0
 chardet==3.0.4
 cliff==2.11.0
 cmd2==0.8.1
 coverage==4.0
-cryptography==2.1
+cryptography==3.0
 debtcollector==1.19.0
 dogpile.cache==0.6.5
 dulwich==0.19.0
@@ -62,7 +62,7 @@ python-memcached==1.59
 python-mimeparse==1.6.0
 python-subunit==1.2.0
 pytz==2018.3
-PyYAML==3.12
+PyYAML==3.13
 requests-mock==1.2.0
 requests==2.14.2
 requestsexceptions==1.4.0

test-requirements.txt

@@ -6,7 +6,7 @@ hacking>=3.0,<4.0.0 # Apache-2.0
 flake8-docstrings==0.2.1.post1 # MIT
 
 coverage!=4.4,>=4.0 # Apache-2.0
-cryptography>=2.1 # BSD/Apache-2.0
+cryptography>=3.0 # BSD/Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
 mock>=2.0.0 # BSD
 oslotest>=3.2.0 # Apache-2.0