extended logging for 'wsdl2java' target to see errors

- the default log level is ERROR (see org.apache.tools.ant.DefaultLogger)

- but Gant uses log level INFO to log errors when running org.apache.cxf.tools.wsdlto.WSDLToJava

- if everything runs fine the output looks like this:
```
Generating java stubs from grails-app/conf/some.wsdl
     [java] Loading FrontEnd jaxws ...
     [java] Loading DataBinding jaxb ...
     [java] wsdl2java -verbose -d src/java -autoNameResolution -validate grails-app/conf/some.wsdl
Completed wsdl2java
```

- if an error occurs it looks like this:
```
  Generating java stubs from grails-app/conf/some.wsdl
     [java] Loading FrontEnd jaxws ...
     [java] Loading DataBinding jaxb ...
     [java] wsdl2java -verbose -d src/java -autoNameResolution -validate grails-app/conf/some.wsdl
     [java] WSDLToJava Error: ...
     [java] SOME STACKTRACE ...
  Completed wsdl2java
```