pycparser-2.14 wheel is wrongly built and raises AssertionError

[Sylvain Bauza]

Most of our gate jobs are impacted (Nova UTs, Tempest tests, Grenade checks) by a new respin of pycparser that raises an AssertionError when imported.

Note that not only Nova but a lot of OpenStack projects are impacted :
http://logstash.openstack.org/#/dashboard/file/logstash.json?query=message:%20\%22AssertionError:%20sorry,%20but%20this%20version%20only%20supports%20100%20named%20groups\%22&from=24h

The issue has been logged upstream https://github.com/eliben/pycparser/issues/147 but we somehow need to downgrade pycparser first in order to stabilize our gates.

[Sylvain Bauza (sylvain-bauza)]

We need to decouple Swift check from upper-constraint modifications as it prevents us to merge the pycparser downgrade because Swift doesn't actually use upper-constraints yet.. https://review.openstack.org/#/c/381031/1