[PATCH] xfstests: Fix hang when mkfs.btrfs isn't present

[Rich Johnston]

This patch has been committed.

Thanks
--Rich

commit 52f4953ac4a377f9f7fc870d2a81f30c3e5d3c7f
Author: Eric Sandeen <sandeen at sandeen.net>
Date:   Tue Mar 5 22:41:54 2013 +0000

     xfstests: Fix hang when mkfs.btrfs isn't present

     My earlier patch (xfstests: handle new mkfs.btrfs -f option cleanly)
     had a flaw in that if set_prog_path mkfs.btrfs returns nothing,
     the grep will hang.

     Test for that case to avoid it, and just return the empty string
     in that case.

     Reported-by: Rich Johnston <rjohnston at sgi.com>
     Signed-off-by: Eric Sandeen <sandeen at redhat.com>
     Reviewed-by: Rich Johnston <rjohnston at sgi.com>
     Signed-off-by: Rich Johnston <rjohnston at sgi.com>