Handle properly missing area files subdir

[rezib]

hpc-config-push fails when an area subdir is missing:

root@<node>:~/ccnhpc/rpalancher# hpc-config-push
[hiera-eyaml-core] Loaded config from /root/.eyaml/config.yaml
Traceback (most recent call last):
  File "/usr/sbin/hpc-config-push", line 1169, in <module>
    main()
  File "/usr/sbin/hpc-config-push", line 1162, in main
    copy_reenc_private_files()
  File "/usr/sbin/hpc-config-push", line 564, in copy_reenc_private_files
    private_files_area_build_dir)
  File "/usr/sbin/hpc-config-push", line 72, in conf_copy
    shutil.copy2(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib/python3.5/shutil.py", line 257, in copy2
    copyfile(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib/python3.5/shutil.py", line 120, in copyfile
    with open(src, 'rb') as fsrc:
FileNotFoundError: [Errno 2] No such file or directory: 'hpc-privatedata/files/<cluster>/user'

It must either ignore the missing dir or print a meaningful error.