Avoid builtins that were removed in Python 3

- `file` was removed in favor of `open`. Switch to the new spelling.
- `buffer` was removed in favor of a buffer protocol (and memoryview),
  and `reload` was moved to importlib.
  Both are used in py2-only blocks, so just placate PyLint.

https://fedorahosted.org/freeipa/ticket/5623

Reviewed-By: Jan Cholasta <jcholast@redhat.com>
Reviewed-By: Martin Basti <mbasti@redhat.com>

ipa-client/ipa-install/ipa-client-install

@@ -1573,7 +1573,7 @@ def do_nsupdate(update_txt):
     root_logger.debug("Writing nsupdate commands to %s:", UPDATE_FILE)
     root_logger.debug("%s", update_txt)
 
-    update_fd = file(UPDATE_FILE, "w")
+    update_fd = open(UPDATE_FILE, "w")
     update_fd.write(update_txt)
     update_fd.flush()
     update_fd.close()

ipalib/cli.py

@@ -40,7 +40,7 @@ if six.PY3:
     unicode = str
 
 if six.PY2:
-    reload(sys)
+    reload(sys)                         # pylint: disable=reload-builtin
     sys.setdefaultencoding('utf-8')     # pylint: disable=no-member
 
 from ipalib import frontend

ipalib/x509.py

@@ -130,7 +130,7 @@ def load_certificate(data, datatype=PEM, dbdir=None):
     initialize_nss_database(dbdir=dbdir)
 
     if six.PY2:
-        return nss.Certificate(buffer(data))
+        return nss.Certificate(buffer(data))  # pylint: disable=buffer-builtin
     else:
         # In python 3 , `bytes` has the buffer interface
         return nss.Certificate(data)