The LibvirtNetVolumeDriver is handling both rbd and
sheepdog (iscsi) connections. The auth config logic
is mingling both backends which is really confusing.
For example, the iscsi protocol only defines auth_method,
auth_username and auth_password. It does not set an
auth_enabled value in the connection_info['data'] dict.
This change simplifies the logic involved for setting
the auth config by decoupling the rbd/iscsi handlers.
A follow-up change will build on this to fix the
rbd auth config to prefer the cinder volume connection_info
auth data over the local config for nova in the case
that different cinder backends are used for ephemeral
and block storage.
Change-Id: I8a55d87f75ecad757ce81b1f5f77c3a551154a17
Partial-Bug: #1635008
5595b4613a