Path specifications in the Metrics Service support a limited
notion of variables for which actual values are substituted
dynamically. The syntax is taken from make:
$(var). The evaluation of such variables is handled by a
user-supplied VariableEvaluator instance. The parsing
and substitution is handled by the Metrics Service.
A useful base-class for classes which implement this interface
StandardVariableEvaluator, which can supply values for
the variables localagent, localnode and
localhost.
String evaluateVariable(String var)