[gparted] Detect btrfstune change UUID capability again (#784467)

[Curtis Gedak <gedakc src gnome org>]

commit 59c8a7d6dfc86f794a89d0759ebae1e117f12b94
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Mon Jul 3 07:25:26 2017 +0100

    Detect btrfstune change UUID capability again (#784467)
    
    Btrfstune changed it's command line help output from being written on
    stderr to being written on stdout in the following commit first included
    in btrfs-progs 4.7.2 released 05-Sep-2016.  This breaks GParted
    detection of the change UUID capability.  Found on the very latest
    distributions: up to date Arch Linux and Fedora 26 Beta.  Fix this.
    
        
https://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git/commit/?id=57d1cbd867311d99a2ae5e3cdcffd04
        btrfs-progs: print help test to stdout
    
    Bug 784467 - No longer detecting btrfs change UUID capability

 src/btrfs.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/btrfs.cc b/src/btrfs.cc
index 19386b9..bd90aaa 100644
--- a/src/btrfs.cc
+++ b/src/btrfs.cc
@@ -111,7 +111,7 @@ FS btrfs::get_filesystem_support()
        if ( ! Glib::find_program_in_path( "btrfstune" ).empty() )
        {
                Utils::execute_command( "btrfstune --help", output, error, true );
-               if ( Utils::regexp_label( error, "^[[:blank:]]*(-u)[[:blank:]]" ) == "-u" )
+               if ( Utils::regexp_label( output + error, "^[[:blank:]]*(-u)[[:blank:]]" ) == "-u" )
                        fs.write_uuid = FS::EXTERNAL;
        }