repository: Allow fetch-all to fail silently

We're seeing odd issues with git fetch returning SSL errors due to the
high number of requests.  Given that the fetch all is occurring to work
around an initial repo sync, failing the build on a fetch all error is a
bit agressive.

BUG=chromium:948151
TEST='cros tryjob --staging samus-paladin-trjob'

Change-Id: I0e2862919ad5321a82f6ece7ad2bd5303ff90cc1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1548397
Reviewed-by: Jason Clinton <jclinton@chromium.org>
Trybot-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Mike Nichols <mikenichols@chromium.org>
Commit-Queue: Mike Nichols <mikenichols@chromium.org>
(cherry picked from commit 6d3728be4d8c9e83dc74a7130eb575e1c609dda9)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1550023
Tested-by: Cindy Bayless <cindyb@chromium.org>
diff --git a/cbuildbot/repository.py b/cbuildbot/repository.py
index a521c31..4044aad 100644
--- a/cbuildbot/repository.py
+++ b/cbuildbot/repository.py
@@ -634,7 +634,7 @@
     if detach:
       cmd.append('--detach')
 
-    cros_build_lib.RunCommand(cmd, cwd=self.directory)
+    cros_build_lib.RunCommand(cmd, cwd=self.directory, error_code_ok=True)
 
   def GetRelativePath(self, path):
     """Returns full path including source directory of path in repo."""