fstests: btrfs add more tests into the scrub group

fstests: btrfs add more tests into the scrub group

I wanted to verify tests using the command "btrfs scrub start" and
found that there are many more test cases using "btrfs scrub start"
than what is listed in the group.list file. So, get them to the scrub
group.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>