tools: put all host-side code into host_tool namespace

To avoid confusion and organize the code itself more cleanly, place the
host-side code into its own namespace.

Change-Id: I573eb0494eb59874adb1d1eadc502499e928e396
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/tools/updater.cpp b/tools/updater.cpp
index b7ea191..6fed1d6 100644
--- a/tools/updater.cpp
+++ b/tools/updater.cpp
@@ -23,6 +23,9 @@
 #include <cstring>
 #include <memory>
 
+namespace host_tool
+{
+
 void updaterMain(BlobInterface* blob, DataInterface* handler,
                  const std::string& imagePath, const std::string& signaturePath)
 {
@@ -95,3 +98,5 @@
 
     return;
 }
+
+} // namespace host_tool