bp: MB-12156 Don't delete buckets when changing datapath.

Change-Id: Ie738291e367e3e136c771086a7c1deb6d45c7dc1
Orig-Reviewed-on: http://review.couchbase.org/41332
Reviewed-on: http://review.couchbase.org/42987
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
bp: MB-12147 Check all required stats for disk/data usage.

We have couch_disk_data_size (as well as some other stats that don't
make sense) even if there're only memmcached buckets. That's because in
certain places we don't make clear separation between memcached and
membase buckets in stats_collector code. I decided that it's easier to
just check all the required stats and fix the referred bug in this way.

Change-Id: Ia1620031aa87245178e205a30f7e97ded2ac7451
Orig-Reviewed-on: http://review.couchbase.org/41379
Reviewed-on: http://review.couchbase.org/42988
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
bp: MB-12158: don't trap exits in dcp_proxy processes

Because we don't really need to.

And most importantly because erlang has a bug where send might get
stuck forever if socket is closed on other end.

So if we just die when dcp_replicator dies we'll avoid this
problem. Or at very least we'll close both sockets without any delays.

Change-Id: Id6143b6157aad641e28cdc783b74a0843d55b118
Orig-Reviewed-on: http://review.couchbase.org/41410
Reviewed-on: http://review.couchbase.org/42989
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
bp: MB-12288:only allow xdcr-over-ssl proxying to memcached data port

Change-Id: Iec6869a2762366283ebabc508879ad2f3ef39763
Orig-Reviewed-on: http://review.couchbase.org/41804
Reviewed-on: http://review.couchbase.org/42990
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>