ws: Clearer data shunting error messages in mock-sshd

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
ws: Check on exit result of mock-sshd and report failures

This helps us find out when mock-sshd is crashing and causing
seemingly unrelated problems in tests.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
ws: A bit cleaner verify of control messages in test-webservice

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
ws: Ignore SIGPIPE in mock-sshd tests

Trying to solve Travis failures here, and this may be the cause
of the /web-service/fail-spawn/rfc6455 and similar tests failing.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
ws: Quiet down the fail_spawn tests in test-webservice

Now that (hopefully) we've finished debugging the issue
we were trying to solve here.

Closes #1004
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>