MB-8189 Start ns_server application as permanent.

application:start defaults to temporary restart type. Which means that
if ns_server application terminates for whatever reason (say
reached_max_restart_intensity), the VM will still survive this and
babysitter won't know that something went wrong.

Change-Id: I59238ab4e332c738a82a70a91b2f4712c2b429d2
Reviewed-on: http://review.couchbase.org/26087
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-8189 Start ns_babysitter application as permanent too.

Hopefully it won't crash but it makes sense to terminate everything if
it does.

Change-Id: I635bbde856a519e7a3846d9ed53e96e6da179077
Reviewed-on: http://review.couchbase.org/26088
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-8189 Start child_erlang in a intermediate supervisor.

The potential problem with current approach is that ep-engine depends
on mccouch. So if for some reason ns_babysitter_sup is trying to
shutdown ns_child_ports_sup while child VM crashes, it will fail
because of this dependency. And at the same time child VM won't be
restarted because supervisor is waiting for ns_child_ports_sup to
terminate. With intermediate supervisor child VM will be restarted and
ep-engine will be able to shutdown.

Change-Id: I231ab390ab8de10dbdde61801769f80eae5bb069
Reviewed-on: http://review.couchbase.org/26089
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>