Adds supports to target DestinationKeyspaceID to handle other

[rafael]

Description

• minor change: for handle other if the target is a keyspaceID, it should be safe to execute it because is by definition a single shard.
• Use case for this is to be able to do queries like this:

   # Let's say we have a shard with two shards -40 ,  40-
   # Before this change, this works:
   use ks/-40
   show tables; 
   # But this does not work:
   use ks[00];
   show tables;
  

• Given that a targeting to a keyspaceID is also a single shard, it seems like this should be supported.

[rafael]

cc: @systay , @harshit-gangal - @sougou mentioned you might be interested in taking a look at this change too.

[setassociative]

Agreed that this should be a safe routing change.