Add new command to test vschema with querylog - plantest

[systay]

Given a querylog and a vschema, it should be possible to test the querylog against the vschema, and get some kind of report out.

The report should say:

• What percentage of queries are single route queries? If we can optimise a query down to a single route, we know it's going to be a fast query
• What percentage of transactions would be single shard transactions, and how many would need distributed transaction handling?