HPCC-9022 Allow testsocket to read query from stdin

Potentially handy for using testsocket via PIPE, for example for roxie query
regression tests.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
HPCC-9022 Allow testsocket to read query from stdin

Minor change following code review

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4261 from richardkchapman/testsocket-stdin

HPCC-9022 Allow testsocket to read query from stdin

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>