add mpi4py helper

python/paddle/fluid/distributed/helper.py

+from mpi4py import MPI
+
+class MPIHelper(object):
+    def __init__(self):
+        self.comm = MPI.COMM_WORLD
+
+    def get_rank(self):
+        return self.comm.Get_rank()
+
+    def get_size(self):
+        return self.comm.Get_size()
+
+    def get_ip(self):
+        import socket
+        local_ip = socket.gethostbyname(socket.gethostname())
+        return local_ip
+
+    def get_hostname(self):
+        import socket
+        return socket.gethostname()