PR #12130 refactored the test to use the `wantPeers` helper, but this
function only returns the number of voting peers, which in this test
should be equal to 2.

I think the tests were passing back them because of a bug in Raft
(https://github.com/hashicorp/raft/pull/483) where a non-voting server
was able to transition to candidate state.

One possible evidence of this is that a successful test run would have
the following log line:

```
raft@v1.3.5/raft.go:1058: nomad.raft: updating configuration: command=AddVoter server-id=127.0.0.1:9101 server-addr=127.0.0.1:9101 servers="[{Suffrage:Voter ID:127.0.0.1:9107 Address:127.0.0.1:9107} {Suffrage:Voter ID:127.0.0.1:9105 Address:127.0.0.1:9105} {Suffrage:Voter ID:127.0.0.1:9103 Address:127.0.0.1:9103} {Suffrage:Voter ID:127.0.0.1:9101 Address:127.0.0.1:9101}]"
```

This commit reverts the test logic to check for peer count, regardless
of voting status.