### Description of problem:

JBoss EAP 6.4 fails to starts up when resolving an expression with the default value containing a '$' at the end.


### How reproducible:

Anytime when setting an expression with the default value containing a '$' at the end.


### Steps to Reproduce:

1. Modify standalone.xml and configure system property which contains the default with  '$' at the end. For example:

    <system-properties>
        <property name="regex_prop_test" value="${my.regex.test:^default$}"/>
    </system-properties>

2. Start JBoss EAP 6.4


### Actual results:

JBoss failed to start-up with the following ERROR message:

~~~
ERROR [org.jboss.as.controller.management-operation] (Controller Boot Thread) JBAS014612: Operation ("add") failed - address: ([("system-property" => "regex_prop_test")]) - failure description: "JBAS013494: Incomplete expression: ${my.regex.test:^default$}"
~~~


### Expected results:

JBoss starts up succesfully without the ERROR message.


### Additional info:

It looks this issue is a regression caused by a new feature https://issues.jboss.org/browse/WFCORE-179, which was incorporated since EAP 6.4.0.

And this issue was reported in the upstream JIRA https://issues.jboss.org/browse/WFCORE-1399 and already fixed in upstream. Please backport the fix to EAP 6.4 branch.


### Workaround:

This issue can be workaround by the following configuration using the new feature "nested expression" introduced by WFCORE-179:

    <system-properties>
        <property name="default_regex" value="^default$"/>
        <property name="regex_prop_test" value="${my.regex.test:${default_regex}}"/>
    </system-properties>