Save dumpstate duration stats so it can be tuned over time.

Fixes: 26373682
Test: dumpstate_test passes and manual verification

Change-Id: I72a308bfb314e157b12746c1be2c33833bdf9d8a
diff --git a/cmds/dumpstate/testdata/stats-invalid-both-NAN.txt b/cmds/dumpstate/testdata/stats-invalid-both-NAN.txt
new file mode 100644
index 0000000..4a9466d
--- /dev/null
+++ b/cmds/dumpstate/testdata/stats-invalid-both-NAN.txt
@@ -0,0 +1 @@
+N_RUNS AVERAGE
\ No newline at end of file