[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: #40196

Closes-Bug: #1886298

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

Change-Id: I643f1f2d97b10cd8b878ea632ef57fcafeb229bf

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==1.14.0
 cliff==2.8.0
 cmd2==0.8.0
 contextlib2==0.4.0
 coverage==4.0
-cryptography==2.1
+cryptography==2.7
 debtcollector==1.2.0
 decorator==3.4.0
 deprecation==1.0
@@ -23,7 +23,7 @@ fixtures==3.0.0
 flake8==2.5.5
 future==0.16.0
 futurist==1.2.0
-greenlet==0.4.10
+greenlet==0.4.15
 hacking==0.12.0
 idna==2.6
 imagesize==0.7.1
@@ -36,7 +36,7 @@ jsonschema==2.6.0
 keystoneauth1==3.4.0
 kombu==4.0.0
 linecache2==1.0.0
-MarkupSafe==1.0
+MarkupSafe==1.1.1
 mccabe==0.2.1
 monotonic==0.6
 mox3==0.20.0
@@ -88,7 +88,7 @@ python-novaclient==9.1.0
 python-openstackclient==3.12.0
 python-subunit==1.0.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==3.13
 repoze.lru==0.7
 requests-mock==1.2.0
 requests==2.14.2

requirements.txt

@@ -8,6 +8,6 @@ oslo.i18n>=3.15.3 # Apache-2.0
 oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 keystoneauth1>=3.4.0 # Apache-2.0
-PyYAML>=3.12 # MIT
+PyYAML>=3.13 # MIT
 requests>=2.14.2 # Apache-2.0
 stevedore>=1.20.0 # Apache-2.0