sql: make type in column-meta be consistent with NoSQL names

Column meta-information which is sent alongside execution result via
IProto protocol, contains string representation of column type.
In some cases, name of type is different from actual type of field. For
instance, if column has type SCALAR, string representation in
meta-information will be "BLOB"; for NUMBER NoSQL type - it will be
"NUMERIC"; for STRING - "TEXT". Instead of this mess, let's always return
exact name of underlying NoSQL type.