Python Library: Fix decorator problem with docstrings
Python Library: Fix decorator problem with docstrings

 * With decorator, the docstring of original method will be deleted.
 * Use functools.wraps() to keep the docstring of original method.
   Check
   http://stackoverflow.com/questions/1782843/python-decorator-problem-with-docstrings
   for detail.

 * With this fix user can check method help message in interactive python with
   command:
    help(lsm.Client.volume_create)

Signed-off-by: Gris Ge <e24f3acbe39bf94f92e8af3c48f8852106ad5ad7@redhat.com>

libstorage/libstoragemgmt,cathay4t/libstoragemgmt,cathay4t/libstoragemgmt,libstorage/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,cathay4t/libstoragemgmt,lazy404/libstoragemgmt,joehandzik/libstoragemgmt,libstorage/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,lazy404/libstoragemgmt,libstorage/libstoragemgmt,jumitche/libstoragemgmt,tasleson/libstoragemgmt,lazy404/libstoragemgmt,joehandzik/libstoragemgmt,cathay4t/libstoragemgmt,jumitche/libstoragemgmt,jumitche/libstoragemgmt,tasleson/libstoragemgmt,joehandzik/libstoragemgmt,tasleson/libstoragemgmt,libstorage/libstoragemgmt,jumitche/libstoragemgmt,lazy404/libstoragemgmt,tasleson/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,cathay4t/libstoragemgmt,joehandzik/libstoragemgmt,tasleson/libstoragemgmt,jumitche/libstoragemgmt