[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: #40186

Closes-Bug: #1886298

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

Change-Id: Ibff0fb285694297f74d82ea8275cd6ca0b857cb2

bindep.txt

@@ -1,3 +1,9 @@
+# This is a cross-platform list tracking distribution packages needed for install and tests;
+# see https://docs.openstack.org/infra/bindep/ for additional information.
+
+libffi-dev [platform:dpkg test]
+libffi-devel [platform:rpm test]
+
 # selenium tests
 firefox [selenium]
 xvfb [selenium platform:dpkg]

lower-constraints.txt

@@ -3,14 +3,14 @@ appdirs==1.3.0
 asn1crypto==0.23.0
 Babel==2.3.4
 cachetools==2.0.0
-cffi==1.7.0
+cffi==1.14.0
 chardet==3.0.4
 cliff==2.8.0
 cmd2==0.8.0
 colorama==0.3.9
 contextlib2==0.4.0
 coverage==4.0
-cryptography==2.1
+cryptography==2.7
 debtcollector==1.2.0
 decorator==3.4.0
 deprecation==1.0
@@ -40,7 +40,7 @@ keystoneauth1==3.4.0
 kombu==4.0.0
 linecache2==1.0.0
 MarkupSafe==1.0
-mccabe==0.2.1
+mccabe==0.6.0
 monotonic==0.6
 msgpack-python==0.4.0
 munch==2.1.0
@@ -71,7 +71,7 @@ pika-pool==0.1.3
 Pint==0.5
 positional==1.2.1
 prettytable==0.7.2
-pycodestyle==2.3.1
+pycodestyle==2.5.0
 pycparser==2.18
 pyinotify==0.9.6
 pymongo==3.0.2
@@ -89,7 +89,7 @@ python-neutronclient==6.7.0
 python-novaclient==9.1.0
 python-swiftclient==3.2.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==3.13
 rcssmin==1.0.6
 repoze.lru==0.7
 requests==2.14.2