pid: zone: add zone id to log name

When a log path is provided, append the zone id to the log so that each
zone will have its own log file.

Change-Id: I56f92669eda23148127f53fd50e119912a24200b
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/pid/zone.hpp b/pid/zone.hpp
index a458011..78ebf0f 100644
--- a/pid/zone.hpp
+++ b/pid/zone.hpp
@@ -54,7 +54,7 @@
     {
         if (tuningLoggingEnabled && !tuningLoggingPath.empty())
         {
-            _log.open(tuningLoggingPath);
+            _log.open(tuningLoggingPath + std::to_string(zone));
         }
     }