fel: Try to detect VM environments and print a warning for those

[n1tehawk]

We try to detect virtual machines by parsing the vendor IDs of all USB devices, and will print a warning message if such an environment is encountered.

[kotc]

Tested-By: @kotc

tested in virtualbox@win7_64 (debian64 gues), vm was detected and warning printed ok

@apritzel: yeah, in cpuinfo: flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc rep_good nopl pni ssse3 sse4_1 hypervisor lahf_lm

[ssvb]

Should we merge this as-is or try to implement @apritzel's suggestion?

[ssvb]

Okay, I will push this to the master branch in a few days.