tests/drivers/ipm/peripheral.mailbox failing sporadically on qemu_x86_64 (timeout)

[nashif]

see https://app.shippable.com/github/zephyrproject-rtos/zephyr/runs/31042/6/tests, the test times out with

***** Booting Zephyr OS zephyr-v1.13.0-3219-gdfc8f0a6d5 *****
starting test - Test IPM
ipm_recv0: 'everything is awesome'
ipm_recv0: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor '

[andyross]

OK, confirmed. I got 3 failures out of 10 tries running this test under load on my CI (-ish) docker instance. Interestingly not one failure in 40 running the same binaries built with the same SDK under the host qemu.

So... plausibly timing related. Could be as simple as a stack overflow that depends on when the interrupt lands, if I'm lucky.

[nashif]

going to mark anything sporadic as medium