health_metric: add tmp storage support

Add the tmp storage support in health config parser and health metric.

Change-Id: Ibb265c28b22d786031ed152d2cc52f40814be984
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/health_metric.cpp b/health_metric.cpp
index ed41fd1..b37698e 100644
--- a/health_metric.cpp
+++ b/health_metric.cpp
@@ -54,6 +54,10 @@
         {
             return std::string(BmcPath) + "/" + PathIntf::read_write_storage;
         }
+        case SubType::storageTmp:
+        {
+            return std::string(BmcPath) + "/" + PathIntf::tmp_storage;
+        }
         default:
         {
             error("Invalid Memory metric {TYPE}", "TYPE",