Fix claim_posix_filesystems to work with bind mounts

claim_posix_filesystems() uses largest path prefix to find the mount
point, and assumes that is the file system the path belongs to. Bind
mounts and symlinks will not work with this method. The current patch
uses device id of path from stat systme call.

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>