[goal] Migrating testing to Ubuntu Focal

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

Bump lower constraints to make testing work for Focal.

Change-Id: I6354e7abe8eece9e1d9c9005ed90faefd53c65b2
Story: #2007865
Task: #40216

lower-constraints.txt

@@ -1,14 +1,14 @@
 appdirs==1.3.0
 asn1crypto==0.23.0
-cffi==1.7.0
+cffi==1.14.0
 cliff==2.8.0
 cmd2==0.8.0
 coverage==4.0
-cryptography==2.1
+cryptography==2.7
 debtcollector==1.2.0
 decorator==4.4.0
 deprecation==1.0
-dogpile.cache==0.6.2
+dogpile.cache==0.8.0
 extras==1.0.0
 fixtures==3.0.0
 future==0.16.0
@@ -55,7 +55,7 @@ python-novaclient==9.1.0
 python-openstackclient==5.2.0
 python-subunit==1.0.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==3.13
 requests==2.14.2
 requests-mock==1.2.0
 requestsexceptions==1.2.0