security: Add digest calculation support in transformation

Change-Id: I8326c19aff580289b5301687351d81fd74af8a83
Refs: #3009
diff --git a/src/security/transform/transform-base.cpp b/src/security/transform/transform-base.cpp
index 936e0ae..60e967b 100644
--- a/src/security/transform/transform-base.cpp
+++ b/src/security/transform/transform-base.cpp
@@ -92,6 +92,14 @@
 }
 
 void
+Transform::flushAllOutput()
+{
+  while (!isOutputBufferEmpty()) {
+    flushOutputBuffer();
+  }
+}
+
+void
 Transform::setOutputBuffer(unique_ptr<OBuffer> buffer)
 {
   BOOST_ASSERT(isOutputBufferEmpty());
@@ -139,9 +147,7 @@
 void
 Transform::finalize()
 {
-  while (!isOutputBufferEmpty()) {
-    flushOutputBuffer();
-  }
+  flushAllOutput();
 }
 
 Source::Source()