dmidecode isn't necessarily installed by default (fedora 20), while
the existing /proc/modules detection works fine. i don't see why we
only need one mechanism, so try both and use which one works.
OHAI-525: reverting part of OHAI-525
Any hope of having tests for this? It'd be nice if you had a test that said "Virtualization plugin when dmidecode is not available detects vbox using kernel modules"
add back in spec for /proc/modules and xen