There is no eventlet in common db code anymore, so, if we want to use
thread pooling for DB API calls, we should use eventlet.tpool.Proxy()
instead of tpool_wrapper() from openstack.common.db.api.
Config option CONF.database.use_tpool was moved from module
nova.openstack.common.db.api to nova.db.api.
Config file `nova.conf.sample` was updated as well.
See also patch to Oslo - I6fa140f2b1f03c43ae7cab98ac8a12d71188af76
Co-Authored-By: Chris Behrens <cbehrens@codestud.com>
Change-Id: Id7de85dce11f5ea61dfccddf80de7800a2bc4e37
6e7680f841