Cap jsonschema 3.2.0 as the minimal version

Previous versions of jsonschema (<3.2.0) doesn't support python 3.8 [1].
Python 3.8 is part of the victoria supported runtimes [2] so we now force
to use jsonschema version 3.2.0 to avoid issues, remove ambiguity and ensure
that everything works with python 3 in general.

[1] https://github.com/Julian/jsonschema/pull/627
[2] https://governance.openstack.org/tc/reference/runtimes/victoria.html#python-runtimes-for-victoria

Change-Id: I68d8c3e3d5157a9ec385813eef37e9c7e17f9ae2

lower-constraints.txt

@@ -21,7 +21,7 @@ hacking==0.10.0
 imagesize==0.7.1
 iso8601==0.1.11
 Jinja2==2.10
-jsonschema==2.6.0
+jsonschema==3.2.0
 kazoo==2.6.0
 keystoneauth1==3.4.0
 kombu==4.0.0

requirements.txt

@@ -23,7 +23,7 @@ networkx>=2.1.0 # BSD
 stevedore>=1.20.0 # Apache-2.0
 
 # Used for structured input validation
-jsonschema>=2.6.0 # MIT
+jsonschema>=3.2.0 # MIT
 
 # For the state machine we run with
 automaton>=1.9.0 # Apache-2.0