Adding test of launch measurements in amd_vtpm.py

[galmasi]

From the code this PR is replacing:

TODO: to ask: where do we store/get allowed measures? Is the format ok?

• The allowed measures are from the measured boot refstate, which is a JSON file, and is represented as a dictionary within keylime.
• It seems to make sense to attach launch measurement checks to measured boot refstates in keylime, since the launch measurement largely overlaps the measured boot information (launch measurement: an amalgamated hash of the guest kernel, guest firmware, guest SVSM ...; measured boot policy: guest firmware, guest kernel, guest grub, guest shim, guest initramfs ...)
• Moreover, since the attestation report (and the launch measurements) are verified during the keylime initial quote, and the measured boot policy is available at this time (having been provided with the keylime tenant add command)
• The current measured boot policy has a flexible format, but I propose we use this:

{
   "hostosboot": [ ... list of allowed kernels and initramfs measurements ... ]   <---- current
   "firmware": [ ... list of firmware measurements ...]  <---- current
   "launch_measurements": [ ... list of measurements allowed ... ] <------- PROPOSED
}

E.g. this is the current value while testing on sl-milan01:

{
  "hostosboots": [
    {
      "tag": "hibinst",
      "shim_authcode_sha256": "0xdbffd70a2c43fd2c1931f18b8f8c08c5181db15f996f747dfed34def52fad036",
      "grub_authcode_sha256": "0xacc00aad4b0413a8b349b4493f95830da6a7a44bd6fc1579f6f53c339c26cb05",
      "kernel_authcode_sha256": "0x424771d6a01447e855a9b1666e5e28279ff49746c1b41614366ce84aeb05abd0",
      "kernel_plain_sha256": "0xd51bdbeb18b0f82a59e6b8fb9eace3e261bd137b2eb23135ec8f55b27f188e00",
      "initrd_plain_sha256": "0x059cc37868d832147d9e5083cad4bf5d060da248478cc2bf6d29e2cf464d6fed"
    }
  ],
  "launch_measurements": [
      "0x12d75089a57e6092c34f1efc8043ee878523836c97c004791de6ca63248671a8737364ebb404014a9b23f3b77275ed7b"
  ]
}

[ruocco]

Looks good. Can you also delete the now pointless measurement_allowed function in keylime/tpm/amd_vtpm.py?