public String getShell() {
        return shell;
    }
Used to support shell specified as a default parameter, e.g.

<pre>
  &lt;cmd&gt;java -jar $HOME/server.jar&lt;/cmd&gt;
</pre>

Read <a href="http://blog.sonatype.com/2011/03/configuring-plugin-goals-in-maven-3/#.VeR3JbQ56Rv">more</a> on
this and other useful techniques.
src/main/java/io/fabric8/maven/docker/config/Arguments.java