compile *.java files only

Summary:
Infer's mvn integration would collect *all* files in `src_roots` and pass them
to `javac`. But these folders may contain non-Java files.

Filter out any file that doesn't end in `.java`.

closes #401
closes #418
closes #442

Reviewed By: martinoluca

Differential Revision: D3741893

fbshipit-source-id: 5c489f9

infer/lib/python/inferlib/capture/mvn.py

@@ -60,7 +60,9 @@ class MavenCapture:
                 for src_root in src_roots:
                     for root, dirs, files in os.walk(src_root):
                         for name in files:
-                            files_to_compile.append(os.path.join(root, name))
+                            if name.endswith(".java"):
+                                path = os.path.join(root, name)
+                                files_to_compile.append(path)
                 source_roots_next = False
 
             elif options_pattern in line: