[PATCH qemu-sanity-check] Add -m/--machine option.

[Richard W.M. Jones]

https://bugzilla.redhat.com/show_bug.cgi?id=1875763

I'm in the middle of testing this on ARM (requires me to fix up my old
Mustang box).  So this hasn't been tested yet on !x86-64.  However I
thought it was worth posting anyway for review.

Rich.