blktrace failed if any CPU is made offline

[George Shuklin <george.shuklin@xxxxxxxxx>]

Step sto reproduce:

1. Boot a multi-core machine
2. Disable second (#1) core (# echo 0 > /sys/devices/system/cpu/cpu1/online)
3. Run blktrace on any device

Expected behaviour: a little less log files

Actual behaviour: FAILED to start thread on CPU 1: 22/Invalid argument