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/test/tools_blob_unittest.cpp b/test/tools_blob_unittest.cpp
index f3a01c1..8205d3a 100644
--- a/test/tools_blob_unittest.cpp
+++ b/test/tools_blob_unittest.cpp
@@ -4,6 +4,8 @@
 
 #include <gtest/gtest.h>
 
+namespace host_tool
+{
 CrcInterface* crcIntf = nullptr;
 
 std::uint16_t generateCrc(const std::vector<std::uint8_t>& data)
@@ -211,3 +213,5 @@
         blob.openBlob("abcd", blobs::FirmwareBlobHandler::UpdateFlags::lpc);
     EXPECT_EQ(0xedfe, session);
 }
+
+} // namespace host_tool