buildman: Ignore conflicting tags

Tags like Series-version are normally expected to appear once, and with a
unique value. But buildman doesn't actually look at these tags. So ignore
conflicts.

This allows bulidman to build a branch containing multiple patman series.

Reported-by: Steve Rae <srae@broadcom.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/patchstream.py b/tools/patman/patchstream.py
index b3e66c3..d630157 100644
--- a/tools/patman/patchstream.py
+++ b/tools/patman/patchstream.py
@@ -355,7 +355,7 @@
 
 
 def GetMetaDataForList(commit_range, git_dir=None, count=None,
-                       series = None):
+                       series = None, allow_overwrite=False):
     """Reads out patch series metadata from the commits
 
     This does a 'git log' on the relevant commits and pulls out the tags we
@@ -367,11 +367,13 @@
         count: Number of commits to list, or None for no limit
         series: Series object to add information into. By default a new series
             is started.
+        allow_overwrite: Allow tags to overwrite an existing tag
     Returns:
         A Series object containing information about the commits.
     """
     if not series:
         series = Series()
+    series.allow_overwrite = allow_overwrite
     params = gitutil.LogCmd(commit_range,reverse=True, count=count,
                             git_dir=git_dir)
     stdout = command.RunPipe([params], capture=True).stdout