runner/executor: Fix error handling at terminating test

Instead of just returning and leaking memory and file descriptors
inform user about an error which occurred and terminate
gracefully.

Signed-off-by: Kamil Konieczny <kamil.konieczny@linux.intel.com>
Reviewed-by: Jan Sokolowski <jan.sokolowski@intel.com>
Reviewed-by: Ryszard Knop <rk@dragonic.eu>