git-pw: Gracefully handle filters closing the stdout pipe

When piping git pw through a pipe to a filter, the filter may close its
stdin early (for instance git pw list -j | head) and the next write to
stdout from git pw will raise an exception:

Traceback (most recent call last):
  File "/home/damien/.local/bin/git-pw", line 912, in <module>
    ret = git_pw.run()
  File "/home/damien/.local/bin/git-pw", line 756, in run
    ret = getattr(self, method)()
  File "/home/damien/.local/bin/git-pw", line 653, in do_list
    print(json.dumps(series))
IOError: [Errno 32] Broken pipe

We do want to play nice with those filters too, to just catch that
IOError with errno set to EPIPE and exit without complaining.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

git-pw/git-pw

@@ -48,6 +48,7 @@
 
 import argparse
 from collections import OrderedDict
+import errno
 import fcntl
 import json
 import os
@@ -753,9 +754,14 @@ class GitPatchwork(object):
     def run(self):
         self.setup()
         method = 'do_' + self.cmd.method_name()
-        ret = getattr(self, method)()
-        ret = 0 if ret is None else ret
-        return ret
+        try:
+            ret = getattr(self, method)()
+            ret = 0 if ret is None else ret
+            return ret
+        except IOError as e:
+            if e.errno != errno.EPIPE:
+                raise
+            return 0
 
 
 class AliasedSubParsersAction(argparse._SubParsersAction):