ceph-rgw-loadbalancer: Fix keepalived master selection

ceph-rgw-loadbalancer: Fix keepalived master selection

While 2ca33641 fixed a bug in the way the `keepalived.conf.j2` template matched
hostnames to set the VRRP `MASTER`/`BACKUP` states, it also introduced a
regression in the case where `virtual_ips` is a list of more than one IP
address.

The previous behavior would result in each host in the `rgwloadbalancers` group
to be `MASTER` for one of the `virtual_ips`, but the new behavior caused the
first host to be `MASTER` for all the IP address in `virtual_ips`.

This commit restores the original behavior.

Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>