firmware: start implementing close method

The close method is used to indicate something is done, for instance,
uploading a firmware image or tarball.

Change-Id: I9e972ea12282e700863d51db497c6294040cd2ca
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/firmware_open_unittest.cpp b/test/firmware_open_unittest.cpp
index 78c5d69..1975740 100644
--- a/test/firmware_open_unittest.cpp
+++ b/test/firmware_open_unittest.cpp
@@ -166,8 +166,7 @@
         1, OpenFlags::write | FirmwareBlobHandler::UpdateFlags::ipmi,
         FirmwareBlobHandler::hashBlobID));
 
-    /* Close the file, currently ignoring its return value. */
-    handler->close(0);
+    EXPECT_TRUE(handler->close(0));
 
     EXPECT_CALL(imageMock1, open(StrEq(FirmwareBlobHandler::hashBlobID)))
         .WillOnce(Return(true));
@@ -210,7 +209,7 @@
     /* Close only active session, to verify it's failing on attempt to open a
      * specific blob_id.
      */
-    handler->close(0);
+    EXPECT_TRUE(handler->close(0));
 
     EXPECT_FALSE(handler->open(
         1, OpenFlags::write | FirmwareBlobHandler::UpdateFlags::ipmi,