machine change form + boot button should work together

[Greg Price]

> Error: Boot loader didn't return any data!

Xavid asked me in the office about this error. He had just installed
the machine from a livecd, and wanted to boot it as an HVM. Turned
out he was doing this by going to the info page, picking the 'HVM'
radio button, and hitting 'Power on'.

Which doesn't work, of course, because that radio button is part of
a different form, the 'Change' form. This is basically a UI bug. It
might be the cause of some of the other 'Boot loader didn't return any
data!' errors we've seen.