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/ipmi_errors.hpp b/tools/ipmi_errors.hpp
index fd1f032..994f837 100644
--- a/tools/ipmi_errors.hpp
+++ b/tools/ipmi_errors.hpp
@@ -4,6 +4,9 @@
 #include <sstream>
 #include <string>
 
+namespace host_tool
+{
+
 class IpmiException : public std::exception
 {
   public:
@@ -22,3 +25,5 @@
   private:
     std::string message;
 };
+
+} // namespace host_tool