tools: blob: implement open blob

Implement the host-side tool's open blob command.

Change-Id: Iee432eae0539015e87969159a3d03761df9f8fb5
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/blob_interface_mock.hpp b/test/blob_interface_mock.hpp
index 8218ed5..fc1b284 100644
--- a/test/blob_interface_mock.hpp
+++ b/test/blob_interface_mock.hpp
@@ -1,9 +1,14 @@
 #include "blob_interface.hpp"
 
+#include <gmock/gmock.h>
+
 class BlobInterfaceMock : public BlobInterface
 {
   public:
     virtual ~BlobInterfaceMock() = default;
     MOCK_METHOD0(getBlobList, std::vector<std::string>());
     MOCK_METHOD1(getStat, StatResponse(const std::string&));
+    MOCK_METHOD2(openBlob,
+                 std::uint16_t(const std::string&,
+                               blobs::FirmwareBlobHandler::UpdateFlags));
 };