nova-manage cell_v2 simple_cell_setup creates an invalid cell0

[Claudiu Belu]

Description
===========

If there are no cells created, nova-manage cell_v2 simple_cell_setup will also create cell0, but it creates it with an invalid database connection string: [1].

Having a database connection string like "mysql+pymysql://root:Passw0rd@127.0.0.1/nova?charset=utf8nova_cell0" will cause the rest of the cell setup to fail, with the following error: [2], as there is no valid charset named "utf8nova_cell0", and the second cell is never created.

This issue has been observed in stable/ocata.

Steps to reproduce
==================

* Have no cells available (delete them).
* run nova-manage cell_v2 simple_cell_setup --transport-url $url

Expected result
===============

* cell0 and a second cell to be created.

Actual result
=============

* cell0 created with a wrong database connection string.
* no second cell.

Environment
===========

* devstack, on stable/ocata.
* n_cpu service disabled (other nova-compute services are being run other nodes).

Logs & Configs
==============

[1] nova-manage: http://paste.openstack.org/show/611813/
[2] simple_cell_setup output(last bits): http://paste.openstack.org/show/611815/