[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)

(cherry picked from commit e86ac440ba248c30a489b0fbf55d2cc7ccff456a)
Signed-off-by: Jirka Kremser <jkremser@redhat.com>

Conflicts:
	modules/plugins/jboss-as-7/src/main/java/org/rhq/modules/plugins/jbossas7/BaseComponent.java