MB-100: report replication docs and design docs in /diag

Because having that information for diagnostics is very handy.

Change-Id: I8bdcfbc95b3e591629648ae025a93d87e15d9939
Reviewed-on: http://review.couchbase.org/25398
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-100: tolerate unknown nodes in master_events formatting

I've found /diag not to work sometimes due to bug in master_events
formatting which assumes all nodes it may ever see in master events
will be known. But that's not true particularly for events from before
node renaming, which refer nodes under old names.

Change-Id: Ia75aa703f428c00dfc22826b23fc3312fedfc7b5
Reviewed-on: http://review.couchbase.org/25399
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>