Gerrit ssh host key must be known to jenkins user

Having zuul dev running has user jenkins, it choked because the Gerrit server ssh host key was not known:

2012-09-27 11:32:27,387 DEBUG zuul.Repo: Cloning from ssh://jenkins@GERRIT_HOST:29418/mediawiki/core to /var/lib/zuul/git/mediawiki/core
2012-09-27 11:32:27,534 ERROR zuul.Merger: Unable to initialize repo for mediawiki/core
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/zuul-1.0-py2.7.egg/zuul/merger.py", line 105, in addProject
    repo = Repo(url, path)
  File "/usr/local/lib/python2.7/dist-packages/zuul-1.0-py2.7.egg/zuul/merger.py", line 32, in __init__
    self._ensure_cloned()
  File "/usr/local/lib/python2.7/dist-packages/zuul-1.0-py2.7.egg/zuul/merger.py", line 39, in _ensure_cloned
    git.Repo.clone_from(self.remote_url, self.local_path)
  File "/usr/lib/python2.7/dist-packages/git/repo/base.py", line 739, in clone_from
    return cls._clone(Git(os.getcwd()), url, to_path, GitCmdObjectDB, progress, **kwargs)
  File "/usr/lib/python2.7/dist-packages/git/repo/base.py", line 691, in _clone
    finalize_process(proc)
  File "/usr/lib/python2.7/dist-packages/git/remote.py", line 64, in finalize_process
    proc.wait()
  File "/usr/lib/python2.7/dist-packages/git/cmd.py", line 100, in wait
    raise GitCommandError(self.args, status, self.proc.stderr.read())
GitCommandError: 'git clone -v ssh://jenkins@GERRIT_HOST:29418/mediawiki/core /var/lib/zuul/git/mediawiki/core' returned exit status 128: Host key verification failed.
fatal: The remote end hung up unexpectedly

At least the debug message is meaningful :-)

The first action would be to update the documentation. Then maybe zuul-server could get a check command that would validate the config files and attempt one connection to the host to make sure everything will work fine.