virtualization tests don't work on arm

Virtualization seems to work completely differently on arm, so all of our tests, which assume x86 conventions and tools, fail to work. Specifically:

- virtualization/virtualization-check: virt_check script looks for /proc/cpuinfo flags which don't exist on arm, and depends on dmidecode for determining memory totals.

- kvm-ok (and the cpu-checker package) are not available for arm, so virtualization/kvm_ok test fails.

- virtualization/kvm_check_vm fails due to absence of kvm:

$ /usr/share/checkbox/scripts/virtualization kvm
Executing KVM Test
WARNING:root:No config file found
I: -input-charset not specified, using utf-8 (detected in locale settings)
Total translation table size: 0
Total rockridge attributes bytes: 331
Total directory bytes: 0
Path table size(bytes): 10
Max brk space used 0
183 extents written (0 MB)
Traceback (most recent call last):
  File "/usr/share/checkbox/scripts/virtualization", line 269, in <module>
    main()
  File "/usr/share/checkbox/scripts/virtualization", line 266, in main
    args.func(args)
  File "/usr/share/checkbox/scripts/virtualization", line 235, in test_kvm
    result = kvm_test.start()
  File "/usr/share/checkbox/scripts/virtualization", line 190, in start
    instance = self.boot_image(self.image)
  File "/usr/share/checkbox/scripts/virtualization", line 134, in boot_image
    universal_newlines=True, shell=False)
  File "/usr/lib/python3.3/subprocess.py", line 820, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.3/subprocess.py", line 1438, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'kvm'

I chose to file this big bug instead of smaller ones since the work to tackle this will probably have to be done in one go, but it can of course be split into several bugs if needed.