Move refresh_server() to nova_utils

Move refresh_server() to nova_utils so Server, Instance, and
CloudServer can use it.

Change-Id: Ib97eead3930a6a7de66ffa6aa4453b2bab80b0c6
Make server resources use nova_utils.refresh_server()

Update Server, Instance, and CloudServer so that they use
nova_utils.refresh_server() instead of server.get().

Change-Id: Id65fabaa15c06ecf511c231888166eded00ba467
Handle API limit exception in nova_utils.refresh_server

novaclient raises an OverLimit exception when a 413 response code (API
limit) is returned from the Nova API.  Previously, this would cause the
stack action to fail.  Log a warning instead.

Change-Id: I52c9dc96b34d0645662d98aaeebb7dabe6956e25
Implements: blueprint improve-api-polling