adding servers to a cluster simultaneously, without waiting for the first to be a member should not be allowed

### Environment info
- Version: **1.10.0-ac201b0**
- Deployment: **AZURE**
- Customer: **QA**

### Actual behavior
1. when trying to add servers to a cluster simultaneously, without waiting for the first to be a member, it fails.  

### Expected behavior
1. we should not allow (or fail) adding servers to a cluster simultaneously

### Steps to reproduce
1. run cluster test.
