hijack.sh: fail if the logger trace is empty

[marc-hb]

Resubmit #383 to new main branch

Does not completely fixes #297 but goes a long way.

Signed-off-by: Marc Herbert marc.herbert@intel.com

[marc-hb]

The less ambitious #629 passed except on BYT where it fails consistently

[marc-hb]

https://sof-ci.01.org/softestpr/PR662/build672/devicetest/ is all green!

[aiChaoSONG]

Note that sof-logger is started by func_lib_start_log_collect in lib.sh, and some cases which only do kernel log check don't call this.

[marc-hb]

and some cases which only do kernel log check don't call this.

if [ "X$SOF_LOG_COLLECT" == "X1" ]; then on line 27 should take care of that case. These tests would have failed otherwise.

Merging, if BYT (or other?) starts failing this test again then the #663 workaround should help.