[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: #40207

Closes-Bug: #1886298

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

Change-Id: Ib0a675e53ad060e9e0f8c6bcdce45f7a870e379c

lower-constraints.txt

@@ -12,12 +12,12 @@ fasteners==0.7.0
 fixtures==3.0.0
 gitdb==0.6.4
 GitPython==1.0.1
-greenlet==0.4.10
+greenlet==0.4.15
 imagesize==0.7.1
 iso8601==0.1.11
 Jinja2==2.10
 linecache2==1.0.0
-lxml==3.4.1
+lxml==4.5.0
 MarkupSafe==1.0
 netaddr==0.7.18
 netifaces==0.10.4
@@ -32,7 +32,7 @@ pyparsing==2.1.0
 python-mimeparse==1.6.0
 python-subunit==1.0.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==3.13
 requests==2.14.2
 rfc3986==0.3.1
 smmap==0.9.0

requirements.txt

@@ -11,9 +11,9 @@ oslo.i18n>=3.15.3 # Apache-2.0
 oslo.utils>=3.33.0 # Apache-2.0
 
 # for the routing notifier
-PyYAML>=3.12 # MIT
+PyYAML>=3.13 # MIT
 
-lxml!=3.7.0,>=3.4.1 # BSD
+lxml>=4.5.0 # BSD
 suds-jurko>=0.6 # LGPLv3+
 eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT
 requests>=2.14.2 # Apache-2.0