Use urandom for heat key generation
Use urandom for heat key generation

Reading from /dev/random can block an virtual machine
even for several minutes, when the entropy pool is empty at the read time.

I have doubts we really need to use /dev/random here.
Even the ssh-keygen uses /dev/urandom by default,
 so the /dev/random is a little bit overkill here.

Change-Id: I6d2c6364c2b445304a33b0140e3cdc6804404b63

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