t8n: write output body to sys.stdout if specified

[danceratopz]

What was wrong?

Specifying --output.body=stdout doesn't write the body to sys.stdout, but rather to a file called "stdout" in the directory specified by --output.basedir, or the current working directory, if unspecified.

Both the Geth and Nimbus t8n tools support specifying "stdout" to --output.body in order to write the txs rlp to the system's stdout. The geth, nimbus and ethereum-spec-evm share a common interface implementation in ethereum/execution-spec-tests; this is a discrepancy in their behavior.

Related to Issue ethereum/execution-spec-tests#268.

How was it fixed?

Write the txs rlp to sys.stdout if --output.body=stdout is specified, otherwise to the specified file. As previously, there is no output for the txs rlp if --output.body is omitted.

Cute Animal Picture

[petertdavies]

Nice catch, one minor quibble.