Fix ConcurrentModificationEx in RpcRegistry.onBucketsUpdated

Fix ConcurrentModificationEx in RpcRegistry.onBucketsUpdated

This was introduced by a recent patch. onBucketsUpdated iterates the
routesUpdateCallbacks however one of the callbacks in receiveGetRouter
removes itself from the list causing the ConcurrentModificationEx.

I changed onBucketsUpdated to first copy the list to an array to prevent
this.

Change-Id: I44c9a89b4b433f711cf4f90bf28e6955d8784f5f
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>
(cherry picked from commit f09d37ec4cce2411eaae11dde18f9ce2d2f14118)