DB2 fails with externaldb template

This jira follows up on RHPAM-2002, specifically for the DB2 externaldb use case.

Quoting tradisso@redhat.com in this comment:

DB2 does not work either

• when non-xa datasource is used (KIE_SERVER_EXTERNALDB_NONXA undefined), the connection URL is not set for Kieserver datasource
• when xa datasource is used (KIE_SERVER_EXTERNALDB_NONXA to false), the Kieserver datasource configuration is is missing some XA parameters:

  <xa-datasource
    jndi-name="java:jboss/datasources/jbpmDS_EJBTimer"
    pool-name="ejb_timer-EJB_TIMER" enabled="true" use-java-context="true"
    statistics-enabled="${wildfly.datasources.statistics-enabled:${wildfly.statistics-enabled:false}}">
    <xa-datasource-property name="DatabaseName">dballo</xa-datasource-property>
    <xa-datasource-property name="DriverType">4</xa-datasource-property>
    <xa-datasource-property name="PortNumber">50000</xa-datasource-property>
    <xa-datasource-property name="ServerName">##SERVER_NAME##</xa-datasource-property>
    <driver>db2</driver>
    <transaction-isolation>TRANSACTION_READ_COMMITTED</transaction-isolation>
    <xa-pool>
      <min-pool-size>10</min-pool-size>
      <max-pool-size>10</max-pool-size>
    </xa-pool>
    <security>
      <user-name>dballo07</user-name>
      <password>dballo07</password>
    </security>
  </xa-datasource>
  <xa-datasource jndi-name="java:jboss/datasources/jbpmDS"
    pool-name="rhpam-RHPAM" enabled="true" use-java-context="true"
    statistics-enabled="${wildfly.datasources.statistics-enabled:${wildfly.statistics-enabled:false}}">
    <xa-datasource-property name="DriverType">4</xa-datasource-property>
    <driver>db2</driver>
    <security>
      <user-name>dballo07</user-name>
      <password>dballo07</password>
    </security>
  </xa-datasource>