Disable jBPM extensions in Kie server for BRMS by default

Kie server for BRMS distribution shouldn't require datasource configuration out of the box as it is supposed to be used just for Drools and OptaPlanner functionality.
Otherwise it can lead errors shown in server log as for example is described in https://issues.jboss.org/browse/BXMSDOC-624 .

This can be achieved by disabling jBPM functionality. To do it we need to set system properties org.jbpm.server.ext.disabled and org.jbpm.ui.server.ext.disabled to "true".
This configuration should be consistent in all BRMS distributions and installer.