btrfs: use full subcommand names

Update the remaining calls to 'btrfs' that use shortened command
names.  Use of full names is recommended to avoid any ambiguities.

Signed-off-by: David Sterba <dsterba@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
2 files changed