StatisticsManager misses nodeadded and noderemoved operations when exceptions occur

Currently the nodeadded and node removed operations are batched along with the stat notification operations.
On exception in the tx chain, all the operations in teh queue are discarded.

This design is applicable to the stats but is not suited for node added and node removed.

Node added and node removed should be applied directly and should not be queued.

Issue is mostly seen with 250+ switches on a 3 node cluster.

This might solve many issues with related to node added and node removed being submitted.