Handle OCC EAGAIN & EREMOTEIO in 4.13

This is a temporary fix until the following issues are completed:
    openbmc/openbmc#2327
    openbmc/openbmc#2329

When an EAGAIN or an EREMOTEIO return code is received by hwmon
from the OCC driver in the 4.13 kernel, they should be translated to
an unavailable sensor(0x00) and failed sensor(0xFF) scaled values
respectively. This will keep the OCC hwmon instance running and allow
applications to continue using these sensors as they were reported under
the mainline openbmc/linux 4.10 kernel.

Tested:
    Verified return codes are caught and sensor value modified

Change-Id: Ie61859863e7d88878caa942e5f5b062acabe67aa
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/mainloop.hpp b/mainloop.hpp
index b62481d..a9ec21e 100644
--- a/mainloop.hpp
+++ b/mainloop.hpp
@@ -76,6 +76,8 @@
         const char* _prefix;
         /** @brief DBus sensors namespace root. */
         const char* _root;
+        /** @brief hwmon instance is for an OCC. */
+        bool _isOCC = false;
         /** @brief DBus object state. */
         SensorState state;
         /** @brief Sleep interval in microseconds. */