Add sys command for powercycle on host shutdown.

The new command will trigger a power cycle the next time the host shuts
down. This can exist in parallel with the existing mechanism to trigger
a power cycle after a specified time interval.

The implementation of host state detection and power cycling is platfrom
specific; the new command will just add a temporary file that marks the
system ready to powercycle on the next shutdown. Usually, a systemd unit
would be enabled by the presence of this file to handle the power
cycling process.

Signed-off-by: Shounak Mitra <shounak@google.com>
Change-Id: I0cc40307748fb996be3f6062d8cba1a4b5049683
diff --git a/handler.hpp b/handler.hpp
index 766ddde..2db83df 100644
--- a/handler.hpp
+++ b/handler.hpp
@@ -53,6 +53,13 @@
     virtual void psuResetDelay(std::uint32_t delay) const = 0;
 
     /**
+     * Arm for PSU reset on host shutdown.
+     *
+     * @throw IpmiException on failure.
+     */
+    virtual void psuResetOnShutdown() const = 0;
+
+    /**
      * Return the entity name.
      * On the first call to this method it'll build the list of entities.
      * @todo Consider moving the list building to construction time (and ignore