hpc-config-push fails when one SFTP server is dead

[rezib]

For example:

[root-admin1-pts2] ~# hpc-config-push 
[hiera-eyaml-core] Loaded config from /root/.eyaml/config.yaml
[hiera-eyaml-core] Loaded config from /root/.eyaml/config.yaml
INFO: Reenc Files: Reencrypted 4962 files, 0 errors
INFO: creating archive /tmp/puppet-config-push/tmp28o7jhkl/infra/puppet-config-environment.tar.xz
WARNING: Configured private modules dir is missing: 'hpc-privatedata/puppet-config/toto/modules'
WARNING: Configured private manifests dir is missing: 'hpc-privatedata/puppet-config/toto/manifests'
INFO: creating archive /tmp/puppet-config-push/tmp28o7jhkl/user/puppet-config-environment.tar.xz
WARNING: Configured private modules dir is missing: 'hpc-privatedata/puppet-config/toto/modules'
WARNING: Configured private manifests dir is missing: 'hpc-privatedata/puppet-config/toto/manifests'
[hiera-eyaml-core] Loaded config from /root/.eyaml/config.yaml
[hiera-eyaml-core] Loaded config from /root/.eyaml/config.yaml
INFO: SFTP push: pushing data on hosts ['service1', 'service2', 'service3', 'service4']
INFO: SFTP push: Finished host 0/4
INFO: SFTP push: Finished host 0/4
INFO: SFTP push: Finished host 0/4
INFO: SFTP push: Finished host 0/4
ERROR: SFTP push: SSH failed to root@service2
INFO: SFTP push: SSH error: Unable to connect to service2: [Errno 113] No route to host.
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 1/4
INFO: SFTP push: Finished host 3/4
INFO: SFTP push: Finished host 4/4
multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/usr/lib/python3.5/multiprocessing/pool.py", line 119, in worker
    result = (True, func(*args, **kwds))
  File "/usr/sbin/hpc-config-push", line 974, in _sftp_push_host
    _sftp_rmrf(sftp_client, conf.destination)
  File "/usr/sbin/hpc-config-push", line 911, in _sftp_rmrf
    if _sftp_is_dir(sftp_client, path):
  File "/usr/sbin/hpc-config-push", line 884, in _sftp_is_dir
    is_dir = stat.S_ISDIR(sftp_client.stat(path).st_mode)
AttributeError: 'NoneType' object has no attribute 'stat'
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/sbin/hpc-config-push", line 1169, in <module>
    main()
  File "/usr/sbin/hpc-config-push", line 1165, in main
    push()
  File "/usr/sbin/hpc-config-push", line 1019, in push
    _push_sftp()
  File "/usr/sbin/hpc-config-push", line 1009, in _push_sftp
    result.get()
  File "/usr/lib/python3.5/multiprocessing/pool.py", line 608, in get
    raise self._value
AttributeError: 'NoneType' object has no attribute 'stat'