[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: #40222

Closes-Bug: #1886298

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

Change-Id: Ib51838017f207ad93d2abb063d965a409a138051

lower-constraints.txt

@@ -3,14 +3,14 @@ appdirs==1.4.3
 asn1crypto==0.23.0
 Babel==2.5.3
 certifi==2018.1.18
-cffi==1.7.0
+cffi==1.14
 chardet==3.0.4
 cliff==2.11.0
 cmd2==0.8.2
 colorama==0.3.9
 contextlib2==0.4.0
 coverage==4.0
-cryptography==2.1
+cryptography==3.0
 debtcollector==1.19.0
 decorator==4.2.1
 deprecation==2.0
@@ -71,7 +71,7 @@ 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==2.2.0
 pyperclip==1.6.0
 python-cinderclient==5.0.0