Deprecate glance_* configuration settings

Create a new section in the configuration file called 'glance'.
Move all of the glance_* configuration settings to this section.

DocImpact

The table below has the changes:

+---------------------------------+----------------------------+
| 'DEFAULT' Section               | 'glance' Section           |
|---------------------------------|----------------------------|
| glance_host                     | host                       |
| glance_port                     | port                       |
| glance_protocol                 | protocol                   |
| glance_api_servers              | api_servers                |
| glance_api_insecure             | api_insecure               |
| glance_num_retries              | num_retries                |
| allowed_direct_url_schemes      | allowed_direct_url_schemes |
+---------------------------------+----------------------------+

UpgradeImpact
The changes are backward compatible.

Change-Id: I829cf006f7e7c53a36f5e12b40f60f875fe8f331
Merge "Deprecate glance_* configuration settings"