os-autoinst does not flush serial console buffer on snapshot reload
When tests fail with kernel backtraces, the stale backtrace will be reported again after snapshot reload and trigger bogus failure even when the next test is successful.
dmesg log: https://openqa.suse.de/tests/10371180/logfile?filename=serial0.txt
Here, the LTP test
cve-2017-18075 triggered kernel warning and failed. But the same kernel warning gets reported again at the end of test
cve-2017-1000111 which was successful and the dmesg log does not show any additional backtraces from it.
This appears to be os-autoinst regression because IIRC kernel backtrace detection used to work fine and only reported errors once.