btrfs: check btrfs-convert with extent and non-extent source

btrfs: check btrfs-convert with extent and non-extent source

This is used to check the source which contains combination of Ext3
files in non-extent format and  Ext4 extent-files. And validate the
file md5sums before and after conversion.

btrfs/012: BTRFS_CONVERT_PROG,E2FSCK_PROG definitions reused from
common/config

Signed-off-by: Lakshmipathi.G <Lakshmipathi.G@giis.co.in>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>