bm_instance: Create a new handler

This OEM handler will get properties from tmpfs to serve over IPMI.

Tested:
~# cat /run/bm-instance/asset-tag
12345
~# ipmitool raw 0x2e 0x32 0x79 0x2b 0x00 0x17 0x00
 79 2b 00 17 05 31 32 33 34 35
...
...
(Verified this works for all 7 sub commands)

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: I191b6f4994d91ada49a3332a8e93a3a305561904
diff --git a/test/handler_mock.hpp b/test/handler_mock.hpp
index 579dfc6..b08cd5e 100644
--- a/test/handler_mock.hpp
+++ b/test/handler_mock.hpp
@@ -71,6 +71,8 @@
                 (const, override));
     MOCK_METHOD(uint16_t, accelGetVrSettings,
                 (::ipmi::Context::ptr, uint8_t, uint8_t), (const, override));
+    MOCK_METHOD(std::string, getBMInstanceProperty, (uint8_t),
+                (const, override));
 };
 
 } // namespace ipmi