Change workdir ?

But, Do you know how change log results directory too ?

Open the soapui***.JAR use by your plugin or your gui software and search for the file :soapui-log4j.xml
This file is a log4 file and it contains a variabl envionnment like this one

...value="${soapui.logroot}soapui-errors.log"

Now you have to define for example for the location of soapui-errors.log the variable soapui.logroot.
In order to do that please refer to the log4j manual.

But if you are using the maven plugin you cand do it like this.
This will resolve PARTIALLY the location of the .log files

 <configuration>
    <soapuiProperties>
     <property>
       <!-- Indicate where are stored Soapui logs
                     but not global-groovy.log wich will be generated at the root of the project.
This things is not documented (understand that it was time consuming to find out that )
          But soapui-3.6.1.jar
       has a log4j configuration name : soapui-log4j.xml which have the following line:
       ...value="${soapui.logroot}soapui-errors.log"..
     -->
     <name>soapui.logroot</name>
     <value>${project.build.directory}/soapui-logs/</value>
     </property>
    </soapuiProperties>  

Some of them have no variable like global-groovy.log. The dirty trick is to edit the .jar with your variable.