project.py: Enable test source attributes in .classpath

In Eclipse Proton, there is a new "Contains test sources" attribute
on source folders.  Test source folders and dependencies are shown
with a darker icon in the build path settings, the package explorer
and other locations.

See the Photon release notes [1] for details.

Add the necessary "test" attribute on the classpathentry.

This has no impact on earlier versions of Eclipse, or IDEs other
than Eclipse; they will simply ignore this attribute.

[1] https://www.eclipse.org/photon/noteworthy/

Change-Id: I9ff701bd2328cc9b6d7c4726ce51dc55345b3810

tools/eclipse/project.py

@@ -128,7 +128,9 @@ def gen_plugin_classpath(root):
         if path.exists(path.join(root, 'src', 'test', 'java')):
             testpath = """
   <classpathentry excluding="**/BUILD" kind="src" path="src/test/java"\
- out="eclipse-out/test"/>"""
+ out="eclipse-out/test">
+    <attributes><attribute name="test" value="true"/></attributes>
+  </classpathentry>"""
         else:
             testpath = ""
         print("""\
@@ -161,6 +163,13 @@ def gen_classpath(ext):
             e.setAttribute('output', out)
         if exported:
             e.setAttribute('exported', 'true')
+        if out and "test" in out:
+            atts = doc.createElement('attributes')
+            testAtt = doc.createElement('attribute')
+            testAtt.setAttribute('name', 'test')
+            testAtt.setAttribute('value', 'true')
+            atts.appendChild(testAtt)
+            e.appendChild(atts)
         doc.documentElement.appendChild(e)
 
     doc = make_classpath()