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/provisioning_session.h

@@ -22,7 +22,7 @@ class ProvisioningSessionImpl;
 // Class which is used to implement the provisioning session state machine.
 class ProvisioningSession {
  public:
-  ~ProvisioningSession();
+  virtual ~ProvisioningSession();
 
   // Process a message from the client device.
   // * |message| is the message received from the client device.
@@ -31,13 +31,16 @@ class ProvisioningSession {
   // * |done| will indicate, upon successful return, whether the provisioning
   //   exchange is complete, and the ProvisioningSession can be deleted.
   // Returns OK if successful, or an appropriate error status code otherwise.
-  ProvisioningStatus ProcessMessage(const std::string& message,
-                                    std::string* response,
-                                    bool* done);
+  virtual ProvisioningStatus ProcessMessage(const std::string& message,
+                                            std::string* response,
+                                            bool* done);
 
   // * Returns a ProvisioneddeviceInfo message containing information about the
   //   type of device being provisioned. May return nullptr.
-  const ProvisionedDeviceInfo* GetDeviceInfo() const;
+  virtual const ProvisionedDeviceInfo* GetDeviceInfo() const;
+
+ protected:
+  ProvisioningSession();  // To enable mocking.
 
  private:
 #ifndef SWIGPYTHON