Description of problem:

If HE deployment fails and the customer needs to repeat it, the setup fails when adding ipv6 rules that already exist.

This is because cleanup just remove ipv4 ones:

ovirt-hosted-engine-setup/src/bin/ovirt-hosted-engine-cleanup
    37	remove_ip_rules(){
    38	    for rule in $(ip rule | grep 10*  | cut -d':' -f1)
    39	    do
    40	        ip rule del prio $rule
    41	    done
    42	}

See:

# ip -6 rule show
0:	from all lookup local 
101:	from fd00:1234:5678:900::1/64 lookup main 
32766:	from all lookup main 

# for rule in $(ip rule | grep 10*  | cut -d':' -f1); do ip rule del prio $rule; done

Still here:
# ip -6 rule show
0:	from all lookup local 
101:	from fd00:1234:5678:900::1/64 lookup main 
32766:	from all lookup main 

The 'ip rule' command won't show that ipv6 rule:
# for rule in $(ip rule | grep 10*  | cut -d':' -f1); do echo $rule; done

We need ip -6 rule:
# for rule in $(ip -6 rule | grep 10*  | cut -d':' -f1); do echo $rule; done
101

Version-Release number of selected component (if applicable):
ovirt-hosted-engine-setup-2.3.13-2.el7ev.noarch (customer)