EqualLogic cinder backend support

1) field-level validation beyond validates :presence => true isn't done yet
2) Wizard UI only supports single EQL backend; for multi-backend the advanced
   config view is required.
@sseago any particular reason to choose? `['<%= @host.deployment.cinder.eqlx_pool %>']` instead of `'<%= [@host.deployment.cinder.eqlx_pool] %>'` or letting `#eqlx_pool` to return array?