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/test/test_health_metric_config.cpp b/test/test_health_metric_config.cpp
index 471bf2b..c13e819 100644
--- a/test/test_health_metric_config.cpp
+++ b/test/test_health_metric_config.cpp
@@ -43,7 +43,8 @@
                 .contains(subType);
 
         case metric::Type::storage:
-            return set_t{metric::SubType::storageReadWrite, metric::SubType::NA}
+            return set_t{metric::SubType::storageReadWrite,
+                         metric::SubType::storageTmp}
                 .contains(subType);
 
         case metric::Type::inode: