Glance: start to use nova's glance configuration section

Commit 4b6e75b5f8037adbf63ac2f03dca17f0c8c0bc08 added support
of a neutron section. This updates the code to make use of
that section.

Change-Id: Ib9a0f2aeb0d91adeb567f79917804f0a89fdb6e1
Merge "Glance: start to use nova's glance configuration section"