client: add filename and line in logging

This is to help to know where the log come from.

Bug: 1061531
Change-Id: I1c172fce98aa4ab746a2b3c0a0de6e39c7faa0fb
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2127186
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Junji Watanabe <jwata@google.com>
Reviewed-by: Junji Watanabe <jwata@google.com>
Cr-Mirrored-From: https://chromium.googlesource.com/infra/luci/luci-py
Cr-Mirrored-Commit: 0007b8debcbd1d1db390b88c764acfa56a3b2696
diff --git a/utils/logging_utils.py b/utils/logging_utils.py
index 14e3c3d..2d185e1 100644
--- a/utils/logging_utils.py
+++ b/utils/logging_utils.py
@@ -183,7 +183,9 @@
   Makes it log in UTC all the time. Prepare a rotating file based log.
   """
   assert not find_stderr(root)
-  formatter = UTCFormatter('%(process)d %(asctime)s %(severity)s: %(message)s')
+  formatter = UTCFormatter(
+      '%(process)d %(asctime)s %(severity)s %(pathname)s %(lineno)d:'
+      ' %(message)s')
 
   # It is a requirement that the root logger is set to DEBUG, so the messages
   # are not lost. It defaults to WARNING otherwise.