Support boot ID

[paulcallen]

relating to #933 This would probably be either copying the file in from the host or mounting it. As the file does not change copying would be easier, but this can be amoung the list of files we copy in at boot.

[vtikoo]

We can also generate a new boot id on Mystikos bootup. We have mechanism to get random bytes, missing parts would be code to format random bytestring into an uuid.