With this patch, dangling and looping symlinks are silently
ignored, while links to files and directories are treated the
same as the underlying file or directory.  This is the same
behavior as both 'directory' and 'netfs' pools.

* src/storage/storage_backend_gluster.c
(virStorageBackendGlusterRefreshVol): Treat symlinks similar to
directory and netfs pools.
Signed-off-by: NEric Blake <eblake@redhat.com>