MB-100: collect master events in vperf rebalance tests

Change-Id: Iaa02abe9fca77522e91da2a64a64b6256fa6c086
Reviewed-on: http://review.couchbase.org/24211
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>