I've been reviewing a change for rTSTW. The change was submited to the master branch, and it was up-to-date. Jenkins always failed because of "the change needs rebasing" (https://gerrit.wikimedia.org/r/#/c/422988/). However the change was perfectly up-to-date. I force merged it, thinking that it was a single-time issue. However further tests uploading changes to that repo always fail on jenkins, even after reverting the force merge. @Legoktm suggested on wikimedia-cloud that this might be a zuul cloner issue being broken. I'd appreciate if you could take a look. Thanks.
Example with `labs/tools/stewardbots` change https://gerrit.wikimedia.org/r/#/c/423010/ , the Zuul merger fails to update from Gerrit:
```
2018-03-30 09:39:36,392 DEBUG zuul.Merger: Merging for change 423010,1.
2018-03-30 09:39:36,393 DEBUG zuul.Merger: Processing refspec refs/changes/10/423010/1 for project labs/tools/stewardbots / master ref Z49dd4cf8e9bc405ea9823e28fd3c4d6e
2018-03-30 09:39:36,400 DEBUG zuul.Merger: Unable to find commit for ref master/Z49dd4cf8e9bc405ea9823e28fd3c4d6e
2018-03-30 09:39:36,400 DEBUG zuul.Merger: No base commit found for (u'labs/tools/stewardbots', u'master')
2018-03-30 09:39:36,400 DEBUG zuul.Repo: Resetting repository /srv/zuul/git/labs/tools/stewardbots
2018-03-30 09:39:36,401 DEBUG zuul.Repo: Updating repository /srv/zuul/git/labs/tools/stewardbots
2018-03-30 09:39:36,518 ERROR zuul.Merger: Unable to reset repo <zuul.merger.merger.Repo object at 0x7feec267b3d0>
Traceback (most recent call last):
File "/usr/share/python/zuul/local/lib/python2.7/site-packages/zuul/merger/merger.py", line 326, in _mergeItem
repo.reset()
File "/usr/share/python/zuul/local/lib/python2.7/site-packages/zuul/merger/merger.py", line 101, in reset
self.update()
File "/usr/share/python/zuul/local/lib/python2.7/site-packages/zuul/merger/merger.py", line 207, in update
origin.fetch(tags=True)
File "/usr/share/python/zuul/local/lib/python2.7/site-packages/git/remote.py", line 743, in fetch
res = self._get_fetch_info_from_stderr(proc, progress)
File "/usr/share/python/zuul/local/lib/python2.7/site-packages/git/remote.py", line 640, in _get_fetch_info_from_stderr
finalize_process(proc, stderr=stderr_text)
File "/usr/share/python/zuul/local/lib/python2.7/site-packages/git/util.py", line 155, in finalize_process
proc.wait(**kwargs)
File "/usr/share/python/zuul/local/lib/python2.7/site-packages/git/cmd.py", line 335, in wait
raise GitCommandError(self.args, status, errstr)
GitCommandError: 'git fetch --tags -v origin' returned with exit code 128
stderr: 'fatal: internal server error
remote: internal server error
fatal: protocol error: bad pack header'
```