Switch to Oslo's config generator

This fixes the sample configuration to contain proper
config groups alongway.

Regenerate sample config with oslo's config generator.

DocImpact: Removes the deprecated memcached_server
option from DEFAULT (now in keystone_authtoken group)

Closes-Bug: #1206650
Closes-Bug: #1260322

Change-Id: I170715bfe6ec7dad9f7317e7bb56cbb68034c4ec
Merge "Switch to Oslo's config generator"