resmoke.py can not start replica sets with more than 7 nodes

If you modify the yaml config for say, integration_tests_replset to have a ReplSetFixture with more than 7 nodes, the test will fail to start because the replica set config will be rejected as invalid for having more than 7 voting members.

Ideally, additional nodes (past the 7 voting members) would be added as non-voting.