NewProvisioningSession expects pkcs8 private key and SHA race fix

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Fix SHA hashing to remove race condition. This change
fixes the implementation by passing in the digest buffer.

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The input to ProvisioningEngine::NewProvisioningSession should be
pkcs8 private key instead of pkcs1 private key

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=151273394

Change-Id: Ibcdff7757b2ac2878ee8b1b88365083964bfa10a

provisioning_sdk/public/python/crypto_utility.py

@@ -8,6 +8,8 @@
 
 """Utility functions for cryptography."""
 
+import logging
+
 from cryptography.hazmat import backends
 from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives import serialization
@@ -18,6 +20,7 @@ def VerifySignature(public_key, signature, data):
   hash_algorithm = hashes.SHA1()
   salt_len = 20
 
+  logging.info('Verying signature.')
   key = serialization.load_der_public_key(
       public_key, backend=backends.default_backend())
   key.verify(signature, data,