rpcserver.py: perf_counter_ns is Python 3.7+

perf_counter_ns is only available in Python 3.7 and later.
Define a lambda for 3.6 and lower.

Fixes: https://pagure.io/freeipa/issue/8891
Signed-off-by: François Cami <fcami@redhat.com>
Reviewed-By: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipaserver/rpcserver.py

@@ -31,6 +31,7 @@ import os
 import time
 import traceback
 from io import BytesIO
+from sys import version_info
 from urllib.parse import parse_qs
 from xmlrpc.client import Fault
 
@@ -72,6 +73,10 @@ from requests.auth import AuthBase
 if six.PY3:
     unicode = str
 
+# time.perf_counter_ns appeared in Python 3.7.
+if version_info < (3, 7):
+    time.perf_counter_ns = lambda: int(time.perf_counter() * 10**9)
+
 logger = logging.getLogger(__name__)
 
 HTTP_STATUS_SUCCESS = '200 Success'