[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: #40199

Closes-Bug: #1886298

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

Change-Id: I5b9054a25f2892c158fa2e0855fc32bd4d3c0bd6

lower-constraints.txt

@@ -4,12 +4,12 @@ appdirs==1.3.0
 asn1crypto==0.23.0
 Babel==2.3.4
 cachetools==2.0.0
-cffi==1.7.0
+cffi==1.14
 cliff==2.8.0
 cmd2==0.8.0
 contextlib2==0.4.0
 coverage==4.0
-cryptography==2.1
+cryptography==3.0
 debtcollector==1.2.0
 decorator==3.4.0
 deprecation==1.0
@@ -81,7 +81,7 @@ pyflakes==0.8.1
 Pygments==2.2.0
 pyinotify==0.9.6
 pymongo==3.0.2
-pyOpenSSL==17.1.0
+pyOpenSSL==19.1.0
 pyparsing==2.1.0
 pyperclip==1.5.27
 pyScss==1.3.7