Update openstack.common.config

- Add generator.py from Oslo
- Add notifier from Oslo
- Add generator bash script used by other projects to generate configuration
files
- Update openstack-common.conf file

The patch https://review.openstack.org/#/c/36493/ needs
to be merged before this one. I'll rebase this patch and
generate the heat configuration.

Fix bug #1183275

Change-Id: Id7f24874b7e3e07d06dcf14bc381b9d630f67fc8
Merge "Update openstack.common.config"