Fix l-c testing for ubuntu focal

As per victoria cycle testing runtime and community goal[1]
we need to migrate upstream CI/CD to Ubuntu Focal(20.04).

- Bump the lower constraints for required deps which added python3.8 support
in their later version.

Story: #2007865
Task: #40206

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

Change-Id: If3ec085184fbba81f455164b803afb6f66e46fd0

lower-constraints.txt

@@ -1,6 +1,6 @@
 appdirs==1.3.0
 coverage==4.0
-cryptography==2.1
+cryptography==2.7
 ddt==1.0.1
 decorator==4.4.1
 doc8==0.8.0
@@ -25,7 +25,7 @@ prometheus-client==0.4.2
 Pygments==2.2.0
 python-mimeparse==1.6.0
 python-subunit==1.0.0
-PyYAML==3.12
+PyYAML==3.13
 requests==2.18.0
 requests-mock==1.2.0
 requestsexceptions==1.2.0

requirements.txt

@@ -2,7 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
-PyYAML>=3.12 # MIT
+PyYAML>=3.13 # MIT
 appdirs>=1.3.0 # MIT License
 requestsexceptions>=1.2.0 # Apache-2.0
 jsonpatch!=1.20,>=1.16 # BSD
@@ -16,6 +16,6 @@ iso8601>=0.1.11 # MIT
 netifaces>=0.10.4 # MIT
 
 dogpile.cache>=0.6.5 # BSD
-cryptography>=2.1 # BSD/Apache-2.0
+cryptography>=2.7 # BSD/Apache-2.0
 
 importlib_metadata>=1.7.0;python_version<'3.8' # Apache-2.0