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

Change-Id: I8d37f92f2d06cca9648f20b40eeae2642d0a91ac
Reviewed-on: http://review.couchbase.org/41332
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-12156 Don't trap exits while change disk paths.

It's not needed and prevents us from a situation where process gets
stuck and wakes up much later (potentially after node became part of a
cluster) and thus invalidates the check that node is not provisioned.

Change-Id: Ie0f9ced83150ddca71781704c05a350dd4b6a271
Reviewed-on: http://review.couchbase.org/41333
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-12167 Hide page fault graphs from UI.

Change-Id: I73e099eb4800427fd52d0227e260b81f4a57f0d6
Reviewed-on: http://review.couchbase.org/41378
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
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: I3f17971f2c532c31e63237eb2f5c6956df95e98d
Reviewed-on: http://review.couchbase.org/41379
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>