Fixes error

  File "/nix/store/lxpsl84km87xpk59nai6a33ihgpfs7qr-glusterfs-3.10.2/libexec/glusterfs/glusterfind/changelog.py", line 105, in populate_pgfid_and_inodegfid
      file_xattrs = xattr.list(p)
  AttributeError: 'module' object has no attribute 'list'

when using `glusterfind pre`.

See: https://bugzilla.redhat.com/show_bug.cgi?id=1489610

Also add patch to correctly log stderr from remote nodes
when glusterfind fails.
This, too, should be removed when fixed upstream.

This fixes:

  Traceback (most recent call last):
    File "/nix/store/7f9arl3f9xyj8sm05mkanh2mlp217192-glusterfs-3.10.2/libexec/glusterfs/glusterfind/changelog.py", line 22, in <module>
      import libgfchangelog
    File "/nix/store/7f9arl3f9xyj8sm05mkanh2mlp217192-glusterfs-3.10.2/libexec/glusterfs/glusterfind/libgfchangelog.py", line 21, in <module>
      libgfc = CDLL("libgfchangelog.so", use_errno=True, mode=RTLD_GLOBAL)
    File "/nix/store/nlyr5ankhi7yvva8zndi718zj37js270-python-2.7.13-env/lib/python2.7/ctypes/__init__.py", line 362, in __init__
      self._handle = _dlopen(self._name, mode)
  OSError: libgfchangelog.so: cannot open shared object file: No such file or directory
  Connection to 10.0.0.2 closed.

when running `glusterfind pre`.

Done by setting PYTHONPATH/LD_LIBRARY_PATH as for the other
Python scripts.

glusterfs service: Ensure dirs needed by `glusterfind` exist