MB-9890: avoid logging states of xdc_vbucket_rep childs
MB-9890: avoid logging states of xdc_vbucket_rep childs

When xdc_vbucket_rep process exits it triggers proc_lib code that
dumps exit reason and other convenience diagnostic. Part of that
diagnostics is dump of neighbor process states that don't trap
exits. And worker sub-processes of xdc_vbucket_rep are such processes
that don't trap exits.

So in order to prevent proc_lib from exposing internals of those
workers, we create them via intermediate processes that do trap exits.

Change-Id: I9a92dacd29fa9655bf840ec4bb225ac6d3b40b45
Reviewed-on: http://review.couchbase.org/42491
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,mschoch/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,nimishzynga/ns_server