Allow _status_timeout to be used for non-nova polling

The error status and not-found exception used for
status_timeout and delete_timeout are specific to nova.

This change makes it possible to override the nova defaults.
Specifically, this will improve the status polling of the
orchestration scenario tests.

Change-Id: Ib55f95ed51ecce3813a57c330e0f936414ec3ff2
Merge "Allow _status_timeout to be used for non-nova polling"