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

oem_certificate_generator/BUILD

@@ -15,10 +15,19 @@ py_binary(
     srcs = ["oem_certificate.py"],
 )
 
+py_library(
+    name = "oem_certificate_generator_helper",
+    srcs = ["oem_certificate_generator_helper.py"],
+    deps = [
+        ":oem_certificate",
+    ],
+)
+
 py_test(
     name = "oem_certificate_test",
     srcs = ["oem_certificate_test.py"],
     deps = [
         ":oem_certificate",
+        ":oem_certificate_generator_helper",
     ],
 )