Randomness in generation of Virtual Machines from pre-built Image
Low entropy for PRNGs is bad.
If you set up a VM by automatized software, you won't have entropy for your PRNG which is not good.

What would be the risk level? Weak cryptographic keys (pretty bad if this is f.ex. a SSH log-in key or someting like this).

Seeding the VM with entropy rich data from the host is the standard solution and will solve the problem.

In my edition of "Cryptography Engineering: Design principals and Practical Applications by Schneier, Fergueson and Kohno" the following solutions are described (for seeding the Fortuna-CSPRNG):


Make the VM-creating system (originally the backup system) PRNG aware -> let it update the PRNG's seed file.
Hash the current time. (originally, again backup system: hash the current time along with the seed file). This works unless the clock's reset and will prevent the PRNG from outputting the same bits. (no high entropy :-( )
Same as 2. but use a counter for each VM you create and hash that instead of the time. (again originally for backups)
Provide entropy via a randomly generated seed file.
Just wait for random events to take place. (if your PRNG implementation is good you can't fully reproduce things like RDRAND output or hard-drive noise) This might take some time and should be last line of defense.


Conclusion: Entropy feeding from the outside is the best option.

I hope this gives you some answers.