Functional gate failing because of `The following mandatory config is unset: san-ip,pure-api-token`

[Aurelien Lourot]

It seems like lp:1836109 has been fixed and now, the charm goes into blocked state after deployment when running the functional tests:

Unit Workload Agent Machine Public address Ports Message
cinder/0* active idle 4 172.16.0.19 8776/tcp Unit is ready
  cinder-mysql-router/0* active idle 172.16.0.19 Unit is ready
  cinder-purestorage/0* blocked idle 172.16.0.19 The following mandatory config is unset: san-ip,pure-api-token

Seen in this review:
https://review.opendev.org/c/openstack/charm-cinder-purestorage/+/826657
https://openstack-ci-reports.ubuntu.com/artifacts/3a8/826657/4/check/focal-xena/3a8bf95/