KVM: selftests: Convert the MONITOR/MWAIT test to use printf guest asserts

Convert x86's MONITOR/MWAIT test to use printf-based guest asserts.  Add a
macro to handle reporting failures to reduce the amount of copy+paste
needed for MONITOR vs. MWAIT.

Link: https://lore.kernel.org/r/20230729003643.1053367-25-seanjc@google.com


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