Change the default dynamic usage to baseUtil

This fixed the unbalanced secondary instances on partially empty
clusters, and helps in general for the cases where real utilisation data
is not available.

Ganeti/HTools/Instance.hs

@@ -97,7 +97,7 @@ create name_init mem_init dsk_init vcpus_init run_init pn sn =
              , pNode = pn
              , sNode = sn
              , idx = -1
-             , util = T.zeroUtil
+             , util = T.baseUtil
              }
 
 -- | Changes the index.

hbal.1

@@ -156,14 +156,17 @@ read load), and sum of primary instance network load. An example of
 how to generate these values for input to hbal would be to track "xm
 list" for instance over a day and by computing the delta of the cpu
 values, and feed that via the \fI-U\fR option for all instances (and
-keep the other metrics as zero). For the algorithm to work, all that
-is needed is that the values are consistent for a metric across all
+keep the other metrics as one). For the algorithm to work, all that is
+needed is that the values are consistent for a metric across all
 instances (e.g. all instances use cpu% to report cpu usage, but they
-could represent network bandwith in Gbps).
+could represent network bandwith in Gbps). Note that it's recommended
+to not have zero as the load value for any instance metric since then
+secondary instances are not well balanced.
 
 On a perfectly balanced cluster (all nodes the same size, all
-instances the same size and spread across the nodes equally), all
-values would be zero. This doesn't happen too often in practice :)
+instances the same size and spread across the nodes equally), the
+values for all metrics would be zero. This doesn't happen too often in
+practice :)
 
 .SS OFFLINE INSTANCES
 
@@ -371,8 +374,15 @@ net_util" where the "_util" parameters are interpreted as numbers and
 the instance name must match exactly the instance as read from
 Ganeti. In case of unknown instance names, the program will abort.
 
-If not given, the default values are zero for all metrics and thus
-dynamic utilisation has no effect on the balancing algorithm.
+If not given, the default values are one for all metrics and thus
+dynamic utilisation has only one effect on the algorithm: the
+equalisation of the secondary instances across nodes (this is the only
+metric that is not tracked by another, dedicated value, and thus the
+disk load of instances will cause secondary instance
+equalisation). Note that value of one will also influence slightly the
+primary instance count, but that is already tracked via other metrics
+and thus the influence of the dynamic utilisation will be practically
+insignificant.
 
 .TP
 .BI "-n" nodefile ", --nodes=" nodefile