Add global config file to keep the default values

Ship a config file under /user/share to keep the default values.
The file nova.conf is now documented an acts as an example config file
that can be modified with user preferences.
Poll for database connection indefinitely
Add the second dhcpbridge-flagfile to nova-dist.conf
remove folsom config vars from nova-dist.conf
Reflect the default [keystone_authtoken] section in /etc/nova/nova.conf

Note all this is done in %build, rather than %prep so that
we don't depend on openstack-utils in prep.

Note this also sets auth_version=v2.0 to avoid http://pad.lv/1154809
Avoid qpid exchange leak