[BZ 1072543] Unable to collect metrics from EAP 6 datasources when a system
properties is used in configuration

max-pool-size and min-pool-size metrics are now recoginzed by common code to
resolve a possible expression. BaseComponent.getValues has been changed in a
way, that we have more granular method called BaseComponent.getMetricValue
which handles single metric request. This method returns new enum called
ReadMetricResult which just represents a return code (if not Success, we may
want to know logical reason why metric was not collected)
Merge pull request #19 from lzoubek/bugs/1072543

[BZ 1072543] Unable to collect metrics from EAP 6 datasources when a system properties is used in configuration