Add new google ipmi sys command: SysHostPowerOff

New google ipmi sys command to let the BMC knows host shutdown,
allow host to gracefully shutdown and disable the watchdog with given
time delay.

Signed-off-by: Yunyun Lin <linyuny@google.com>
Change-Id: I02171c9cfed57ae5d10d66b515e4ab7ee8856466
diff --git a/handler.hpp b/handler.hpp
index 1a2cbae..f4b1bbd 100644
--- a/handler.hpp
+++ b/handler.hpp
@@ -109,6 +109,14 @@
      */
     virtual std::tuple<std::uint32_t, std::string>
         getI2cEntry(unsigned int entry) const = 0;
+
+    /**
+     * Set the Host Power Off delay.
+     *
+     * @param[in] delay - delay in seconds.
+     * @throw IpmiException on failure.
+     */
+    virtual void hostPowerOffDelay(std::uint32_t delay) const = 0;
 };
 
 } // namespace ipmi