Rebalance hangs at 100% with error ebucketmigrator_srv:init ... {error,econnrefused}

Incremental rebalance test hanging at 100%. diags show similar error messages as (MB-4824)

For some reason we're only seeing this behavior with our ubuntu cluster.

=========================CRASH REPORT=========================
crasher:
initial call: ebucketmigrator_srv:init/1
pid: <0.16657.0>
registered_name: []
exception error: no match of right hand side value

in function ebucketmigrator_srv:connect/4
in call from ebucketmigrator_srv:init/1
ancestors: ['ns_vbm_sup-default','ns_memcached_sup-default',
'single_bucket_sup-default',<0.14785.0>]
messages: []
links: Port<0.36196>,<0.14807.0>
dictionary: []
trap_exit: false
status: running
heap_size: 610
stack_size: 24
reductions: 1263
neighbours:

test case:
./testrunner resources/jenkins/ubuntu-64-6-nodes.ini -t viewtests.ViewRebalanceTests.test_view_stop_start_incremental_rebalance
(http://qa.hq.northscale.net/job/ubuntu-64-view-longtests/)