patman: Allow commands to raise on error, or not

Make raise_on_error a parameter so that we can control which commands
raise and which do not. If we get an error reading the alias file, just
continue.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/gitutil.py b/tools/patman/gitutil.py
index 77907c1..33743dd 100644
--- a/tools/patman/gitutil.py
+++ b/tools/patman/gitutil.py
@@ -359,7 +359,8 @@
     Returns:
         Filename of git alias file, or None if none
     """
-    fname = command.OutputOneLine('git', 'config', 'sendemail.aliasesfile')
+    fname = command.OutputOneLine('git', 'config', 'sendemail.aliasesfile',
+            raise_on_error=False)
     if fname:
         fname = os.path.join(GetTopLevel(), fname.strip())
     return fname