Add suppport for retrieving machine name

This adds support for reading /etc/os-release, parsing out
OPENBMC_TARGET_MACHINE and returning this to the caller.

Change-Id: If2a419b9a77597686f5137efce97b1150142f181
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/handler_impl.hpp b/handler_impl.hpp
index b9946a1..130a4b0 100644
--- a/handler_impl.hpp
+++ b/handler_impl.hpp
@@ -28,6 +28,7 @@
     VersionTuple getCpldVersion(unsigned int id) const override;
     void psuResetDelay(std::uint32_t delay) const override;
     std::string getEntityName(std::uint8_t id, std::uint8_t instance) override;
+    std::string getMachineName() override;
     void buildI2cPcieMapping() override;
     size_t getI2cPcieMappingSize() const override;
     std::tuple<std::uint32_t, std::string>