pm_test script error leading to uncomputable suspend/resume times

When running job power-management/suspend_30_cycles_with_reboots, which executes script pm_test, we get the following logs in the session directory:

- fwts.log: output of all the consecutive calls to fwts, including all the suspend/resume timings without any issue
- fwts.log.log: a file that contains only "================================= Iteration x ==================================" 30 times
- pm_test.reboot.3.log: the log file generated by the job that should contain, among other things, the average time to sleep/resume.

Even though the data is present in fwts.log, in pm_test.reboot.3.log we see:

Average time to sleep: N/A
Average time to resume: N/A

Because of this, the job `power-management/suspend-30-cycles-time-checks-with-reboots` fail.

After investigation, it looks like the culprit is the pm_test script itself that adds a ".log" extension to a script call that already adds this extension. This creates the file fwts.log.log and, more importantly, prevents the proper retrieval of the suspend and resume times to compute the average!