HotRod connector is not able to resolve expression for external-host in JDG6

Issue

• We need to form a cluster between two nodes both running behind a bridged network (using docker), but it is not possible to set the external address to a system property. We need this so that state transfer indications over hotrod tell the clients to connect to the "external" ip instead of a node local ip. Configuration and error like followed:

<system-properties>
    <property name="infinispan.external_host" value="1.2.3.4"></property>
</system-properties>
...
<subsystem xmlns="urn:infinispan:server:endpoint:6.1">
    <hotrod-connector cache-container="clustered" socket-binding="hotrod">
        <topology-state-transfer  external-host="${infinispan.external_host}" ...></topology>
    </hotrod-connector>
    ..........
</subsystem>

TRACE AbstractTransport:34 - Read string is: ${infinispan.external_addr}
TRACE AbstractTransport:34 - Read string is: ${infinispan.external_addr}
TRACE TcpTransport:211 - Offset: 0, len=2, size=2
TRACE TcpTransport:211 - Offset: 0, len=2, size=2
TRACE TcpTransport:231 - Successfully read array with size: 2
14:31:32 TRACE TcpTransport:231 - Successfully read array with size: 2
14:31:32 TRACE TcpTransport:180 - Read byte 3 from socket input in Socket[addr=localhost/127.0.0.1,port=11222,localport=55162]
   ............
INFO  Codec21:413 - ISPN004006: localhost/127.0.0.1:11222 sent new topology view (id=0, age=0) containing 1 addresses: [${infinispan.external_host}:11222]
INFO  Codec21:413 - ISPN004006: localhost/127.0.0.1:11222 sent new topology view (id=0, age=0) containing 1 addresses: [${infinispan.external_host}:11222]
TRACE TcpTransportFactory:371 - Current list: [localhost/127.0.0.1:11222]
TRACE TcpTransportFactory:371 - Current list: [localhost/127.0.0.1:11222]
TRACE TcpTransportFactory:372 - New list: [${infinispan.external_host}:11222]
TRACE TcpTransportFactory:372 - New list: [${infinispan.external_host}:11222]
TRACE TcpTransportFactory:373 - Added servers: [${infinispan.external_host}:11222]
TRACE TcpTransportFactory:373 - Added servers: [${infinispan.external_host}:11222]
TRACE TcpTransportFactory:374 - Removed servers: [localhost/127.0.0.1:11222]
TRACE TcpTransportFactory:374 - Removed servers: [localhost/127.0.0.1:11222]
INFO  TcpTransportFactory:384 - ISPN004014: New server added(${infinispan.external_host}:11222), adding to the pool.
INFO  TcpTransportFactory:384 - ISPN004014: New server added(${infinispan.external_host}:11222), adding to the pool.
TRACE TcpTransport:75 - Could not connect to server: ${infinispan.external_host}:11222
java.net.UnknownHostException