KVM: selftests: Convert x86's nested exceptions test to printf guest asserts

Convert x86's nested exceptions test to printf-based guest asserts, and
use REPORT_GUEST_ASSERT() instead of TEST_FAIL() so that output is
formatted correctly.

Link: https://lore.kernel.org/r/20230729003643.1053367-26-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>