ewaol-tests: Improve handling of Expect script time-outs

This patch ensures that all unexpected time-outs which occur during the
execution of the expect scripts are reported. Further, the script now returns an
appropriate exit code (124) if the timeout should be considered fatal, which is
subsequently included in the integration test log.

Issue-Id: SCM-3910
Signed-off-by: Richard Neill <richard.neill@arm.com>
Change-Id: I6192a92d3b1a3239fabfda3bfd303a568168078e