xfstests: resolve symlinked devices to real paths

xfstests: resolve symlinked devices to real paths

If you try running xfstests on lvm volumes which are symlinks,
it'll fail to run several tests because our _require_scratch
framework ultimately uses lstat not stat, and does not think
the lvm device (which is usually a symlink to a dm-X device)
is a block device.  Sigh.

Last try at this - just resolve any symlinked devicenames
into their realpath(3) in common.config.

This actually seems to work.

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>