MB-100 fix for rebalance getting stuck
MB-100 fix for rebalance getting stuck

need to trap exits during spawn_and_wait call
and do the proper cleanup after the call

Change-Id: I073b5f9c1b208fbbc2a88f6ca020b31ef203b20d
Reviewed-on: http://review.couchbase.org/35056
Tested-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

mschoch/ns_server,nimishzynga/ns_server,daverigby/ns_server,nimishzynga/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,nimishzynga/ns_server,membase/ns_server,mschoch/ns_server,membase/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,mschoch/ns_server,daverigby/ns_server,daverigby/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,daverigby/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,daverigby/ns_server