Allow longer Class-Path entries (#23269)

jar Class-Path entries have a max line length which, when
exceeded, will cause java to fail to start. Use newline plus
extra space to support large numbers of jar files.

sdks/python/apache_beam/utils/subprocess_server.py

@@ -325,7 +325,7 @@ def make_classpath_jar(cls, main_jar, extra_jars, cache_dir=None):
           manifest.write(b'Manifest-Version: 1.0\n')
           manifest.write(main_class)
           manifest.write(
-              b'Class-Path: ' + ' '.join(classpath).encode('ascii') + b'\n')
+              b'Class-Path: ' + '\n  '.join(classpath).encode('ascii') + b'\n')
       os.rename(composite_jar + '.tmp', composite_jar)
     return composite_jar