Statsd dumpsys handles multiple and saved configs

Statsd dumpsys wasn't handling multiple configs properly. Also, doing a
dump would delete the data that had been saved to disk. This cl fixes
both those issues.

Test: run cts-dev -m CtsStatsdHostTestCases -t android.cts.statsd.atom.HostAtomTests#testDumpsysStats
Change-Id: I5f2f86c70fbcbc1407aae1b1ffeb7fbdb9f67d0e
diff --git a/cmds/statsd/src/StatsService.cpp b/cmds/statsd/src/StatsService.cpp
index 04173b2..bd20728 100644
--- a/cmds/statsd/src/StatsService.cpp
+++ b/cmds/statsd/src/StatsService.cpp
@@ -296,6 +296,7 @@
                                  ADB_DUMP, &proto);
         proto.end(reportsListToken);
         proto.flush(out);
+        proto.clear();
     }
 }