ovsdb-idlc: Generate new *_get_for_uuid() functions.

This allows a client to obtain the IDL version of a row given its UUID.
It isn't normally useful, but there's a specialized use case for getting
the IDL version of a row given the UUID returned by
ovsdb_idl_txn_get_insert_uuid() following transaction commit.

An alternative would be to generate table-specific versions of
ovsdb_idl_txn_get_insert_uuid().  That seems reasonable to me too.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Andy Zhou <azhou@nicira.com>