Adding BlacklistedTablesMap to the shard record.

That way it survives tablets being scrapped.
Add SetShardBlacklistedTables, remove SetBlacklistedTables.
Removing remote action SetBlacklistedTables.
Removing BlacklistedTables from tablet.

And adding test for BlacklistedTablesMap in shard.
Small optimization: do not read shard record if not serving.

We only use shardInfo for master, replica, rdonly.
Fixing a couple comments.
Merge branch 'master' of github.com:youtube/vitess