x86 reverse-debugging test is unreliable
Description of problem:
The reverse-debugging test for the x86 target is not working reliably. If the host system is under load, the test simply hangs and finally times out.
Steps to reproduce:
1. ``make check-venv``
2. Run something in the background that keeps all CPUs busy
3. ``for ((x=0;x<10;x++)); do QEMU_TEST_FLAKY_TESTS=1 pyvenv/bin/avocado run tests/avocado/reverse_debugging.py:ReverseDebugging_X86_64.test_x86_64_pc  ; done``