Nova services may reasonably expect cell databases to exist when they
start. The current cell setup tasks in kolla run after the nova
containers have started, meaning that cells may or may not exist in the
database when they start, depending on timing. In particular, we are
seeing issues in kolla CI currently with jobs timing out waiting for
nova compute services to start. The following error is seen in the nova
logs of these jobs, which may or may not be relevant:

No cells are configured, unable to continue

This change creates the cell0 and cell1 databases prior to starting nova
services.

In order to do this, we must create new containers in which to run the
nova-manage commands, because the nova-api container may not yet exist.
This required adding support to the kolla_docker module for specifying a
command for the container to run that overrides the image's command.

We also add the standard output and error to the module's result when a
non-detached container is run. A secondary benefit of this is that the
output of bootstrap containers is now displayed in the Ansible output if
the bootstrapping command fails, which will help with debugging.

Change-Id: I2c1e991064f9f588f398ccbabda94f69dc285e61
Closes-Bug: #1808575