BQ sink validate output table schema even though truncating table is set, while ideally (please verify) the validation should be skipped when truncating the table.
We should skip this whole section  when  truncating is true
Removed schema validation from BQ sink when 'truncate table' option is set.
comment from BQ java client.
[Experimental] Returns options allowing the schema of the destination table to be updated as a
side effect of the load job. Schema update options are supported in two cases: when
writeDisposition is WRITE_APPEND; when writeDisposition is WRITE_TRUNCATE and the destination
table is a partition of a table, specified by partition decorators. For normal tables,
WRITE_TRUNCATE will always overwrite the schema.
Validated on staging on Jun 25th rc10.