BZ#1144050 - Create cinder backend types

https://bugzilla.redhat.com/show_bug.cgi?id=1144050

Allow creation of cinder backend types. For multi-instance EQLX
backends, allow both sharing the same name and having different
backend names per instance.
Don't use '_backend' suffix for Cinder backend names

We reuse Cinder backend names for Cinder type names, to ensure that
each backend defined in the config file will have its type
created. It's a bit nicer to type

`cinder create --display-name vol1 --volume-type nfs 5`

than

`cinder create --display-name vol1 --volume-type nfs_backend 5`

so the default backend names now don't have the '_backend' suffix.