MB-10660 wrap update_vbucket_state into spawn_rebalance_subprocess
MB-10660 wrap update_vbucket_state into spawn_rebalance_subprocess

to prevent janitor_agent from being stuck if replication_manager
gets stuck

Change-Id: I2333117e69abaf426c1021088112ad8832de90a1
Reviewed-on: http://review.couchbase.org/35034
Tested-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

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