restapi: correct status code for add brick when volume is down.

In Method resolveCreatedList for populating entity,
populate method is used instead of doPopulate.
As doPopulate doesnot return proper status code
when the volume is down.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1018904
Change-Id: Ic6c680383ea75d898a6496c86daabe38630f9d18
Signed-off-by: ndarshan <dnarayan@redhat.com>