btrfs-progs: tests: Add '-o loop' to mount command line in convert-tests.sh
To fix following bug:
# ./convert-tests.sh
[TEST] ext2 4k nodesize, btrfs defaults
failed: mount /root/btrfsprogs/tests/test.img /root/btrfsprogs/tests/mnt
# tail convert-tests-results.txt
...
############### mount /root/btrfsprogs/tests/test.img /root/btrfsprogs/tests/mnt
mount: /root/btrfsprogs/tests/test.img is not a block device (maybe try `-o loop'?)
failed: mount /root/btrfsprogs/tests/test.img /root/btrfsprogs/tests/mnt
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>