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

Change-Id: Ic03cbce17f36a139d90275ab04fab285edf4d2f8

Author: 4383

requirements.txt

@@ -1,7 +1,7 @@
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 requests>=2.14.2 # Apache-2.0
 stevedore>=1.20.0 # Apache-2.0
-jsonschema>=2.6.0 # MIT
+jsonschema>=3.2.0 # MIT
 
 # Oslo Packages
 oslo.i18n>=3.15.3 # Apache-2.0