Make sure execute SLAVEOF command in the right order in psync2 test. (#9316)

The psync2 test has failed several times recently.
In #9159 we only solved half of the problem.
i.e. reordering of the replica that's already connected to
the newly promoted master.

Consider this scenario:
0 slaveof 2
1 slaveof 2
3 slaveof 2
4 slaveof 1
0 slaveof no one, became a new master got a new replid
2 slaveof 0, partial resync and got the new replid
3 reconnect 2, inherit the new replid
3 slaveof 4, use the new replid and got a full resync

And another scenario:
1 slaveof 3
2 slaveof 4
3 slaveof 0
4 slaveof 0
4 slaveof no one, became a new master got a new replid
2 reconnect 4, inherit the new replid
2 slaveof 1, use the new replid and got a full resync

So maybe we should reattach replicas in the right order.
i.e. In the above example, if it would have reattached 1, 3 and 0 to
the new chain formed by 4 before trying to attach 2 to 1, it would succeed.

This commit break the SLAVEOF loop into two loops. (ideas from oran)

First loop that uses random to decide who replicates from who.
Second loop that does the actual SLAVEOF command.
In the second loop, we make sure to execute it in the right order,
and after each SLAVEOF, wait for it to be connected before we proceed.

Co-authored-by: Oran Agra <oran@redislabs.com>