Do not include test themes in theme jar (#13634)

Change-Id: Id3cc353b1e74fa51326ce84d33e741227f98f9b0

themes/build.xml

@@ -18,6 +18,8 @@
     <union id="jar.includes">
         <fileset dir="${result.dir}">
             <include name="VAADIN/themes/**" />
+            <exclude name="VAADIN/themes/*-tests*/**" />
+            <exclude name="VAADIN/themes/tests-*/**" />
         </fileset>
     </union>