Unify REST responses for Acknowledged[Request|Response]

All Rest handlers that use AcknowledgedResponse look identical. Since
we gonna have more of them in the future we can abstract the logic away.
CompletionFieldMapper: Return error if weight is no integer

In order to make sure that people do not get confused, if they
index a float as weight, it makes more sense to reject it instead of
silently parsing it to an integer and using it.

The CompletionFieldMapper now checks for the type of the number which
is being read and throws and exception if the number is something else
than int or long.

Closes #3977
Re-apply pull-request #3956 now that the CLA has been signed.
Don't use TransportClient on FullClusterRestartTests

There seems to be an issue with this test since it shuts down random
nodes and TransportClients seem to be confused due to that. For
now we disable them to figure out if this is the cause of the sporadic
timeouts.