Display unaccounted time in "DevStack Component Timing"

In the "DevStack Component Timing" section, display the unaccounted
time.

Also add the units (seconds) to the output to make it clear to viewers.

Change-Id: Iaca82cc54a355f7077e20e548b771e53387f6628
diff --git a/functions-common b/functions-common
index 4fc7c6d..f2b8d98 100644
--- a/functions-common
+++ b/functions-common
@@ -2270,11 +2270,13 @@
 function time_totals {
     local elapsed_time
     local end_time
-    local len=15
+    local len=20
     local xtrace
+    local unaccounted_time
 
     end_time=$(date +%s)
     elapsed_time=$(($end_time - $_TIME_BEGIN))
+    unaccounted_time=$elapsed_time
 
     # pad 1st column this far
     for t in ${!_TIME_TOTAL[*]}; do
@@ -2291,16 +2293,19 @@
     echo
     echo "========================="
     echo "DevStack Component Timing"
+    echo " (times are in seconds)  "
     echo "========================="
-    printf "%-${len}s %3d\n" "Total runtime" "$elapsed_time"
-    echo
     for t in ${!_TIME_TOTAL[*]}; do
         local v=${_TIME_TOTAL[$t]}
         # because we're recording in milliseconds
         v=$(($v / 1000))
         printf "%-${len}s %3d\n" "$t" "$v"
+        unaccounted_time=$(($unaccounted_time - $v))
     done
+    echo "-------------------------"
+    printf "%-${len}s %3d\n" "Unaccounted time" "$unaccounted_time"
     echo "========================="
+    printf "%-${len}s %3d\n" "Total runtime" "$elapsed_time"
 
     $xtrace
 }