HPCC-11773 Regression test engine crash when ECL throws connection
failed exception

Implement connection error handling.

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>
Merge pull request #6132 from AttilaVamos/HPCC-11773-fix

HPCC-11773 Regression test engine crash when ECL throws connection

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>