Explicitly secure rw perms for recovery.conf at creation time (#910)

We don't want anybody except patroni/postgres user reading this file, it contains replication user and password.

patroni/postgresql.py

@@ -5,6 +5,7 @@ import re
 import shlex
 import shutil
 import socket
+import stat
 import subprocess
 import tempfile
 import time
@@ -1186,6 +1187,7 @@ class Postgresql(object):
 
     def write_recovery_conf(self, recovery_params):
         with open(self._recovery_conf, 'w') as f:
+            os.chmod(self._recovery_conf, stat.S_IWRITE | stat.S_IREAD)
             for name, value in recovery_params.items():
                 f.write("{0} = '{1}'\n".format(name, value))