fuse: detect fusepy module

fuse: detect fusepy module

When importing 'fuse', we might get either the libfuse or
the fusepy module, the latter doesn't have __version__ so
we just print

  error: fuse module is too old for fuse.__version__

but that's misleading. Detect if we have fuse.FUSE and in
that case instead print

  error: fuse module appears to be fusepy, not python-fuse
         please install https://github.com/libfuse/python-fuse

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Rob Browning <rlb@defaultvalue.org>
[rlb@defaultvalue.org: adjust commit message and error messages]
Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>