btrfs: test log replay with qgroups enabled and orphan roots

btrfs: test log replay with qgroups enabled and orphan roots

Test that replaying a log tree when qgroups are enabled and orphan roots
(deleted snapshots) exist, the replay process does not crash.

This is motivated by a bug found in btrfs, introduced in the linux kernel
4.4 release, and is fixed by the linux kernel commit 909c3a22da3b
("Btrfs: fix loading of orphan roots leading to BUG_ON") that landed in
kernel 4.5.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>