tests/xe_eudebug_online: Add set-breakpoint-sigint-debugger test

Add a test that sends SIGINT to the debugger thread with random timing
and checks if nothing breaks, exercising the scenario multiple times.

v2: Count correctly timed SIGINTs and assert that they happened (Mika)
v3: Move loop_count increment outside macro (Mika)

Signed-off-by: Dominik Karol Piątkowski <dominik.karol.piatkowski@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>