Add project reader to account-generator

Tempest requires project_reader to sucessfully run some tests [1].
However, account-generator does not support generating project reader accounts.

This patch therefore changes accout-generator so that it generates
project reader together with other accounts.

[1] https://review.opendev.org/c/openstack/tempest/+/871210

Change-Id: Ie127c2ed159da8a6bc780919cdd4def44e457efb
2 files changed