Fix cpuspeed for low loads (#1618)

This contains 2 fixes for low loaded nodes that have very dynamic
frequency.

Closes #1617

plugins/node.d.linux/cpuspeed

@@ -18,8 +18,20 @@ None needed by default.
 You can set one environment variable to modify the plugins behaviour:
 
   [cpuspeed]
+     env.sleep .2
      env.scaleto100 yes
 
+Parameter sleep 
+
+Sleep for some (fractional) seconds before actually taking the measure.
+This is useful to enable the CPU to relax a little from the previous plugins.
+
+"env.sleep .2" will cause a 200ms sleep.
+
+Default is to NOT sleep, aka "env.sleep 0".
+
+Parameter scaleto100
+
 Show the frequency as a percentage instead of absolute frequency.
 If set the "yes" the plugin sets up a CDEF to change the speed in Hz
 to percent.
@@ -155,6 +167,7 @@ if [ "$1" = "config" ]; then
             echo "cpu$N.min 0"
         elif [ -r "$c/cpufreq/cpuinfo_min_freq" ]; then
             MINHZ=$(cat "$c/cpufreq/cpuinfo_min_freq")
+            MINHZ=$(( $MINHZ - $MINHZ / 10 ))
             echo "cpu$N.min $MINHZ"
         fi
 
@@ -165,6 +178,8 @@ if [ "$1" = "config" ]; then
     if [ "${MUNIN_CAP_DIRTYCONFIG:-0}" != 1 ]; then exit 0; fi
 fi
 
+[ -z "${sleep}" ] || sleep "${sleep}"
+
 for c in /sys/devices/system/cpu/cpu[0-9]*; do
     N=${c##*/cpu}
     if [ IS_RYZEN ] && [ -r "$c/cpufreq/scaling_cur_freq" ]; then