Description of problem:

User unable to create a HCP cluster when availability zone of a machine pool's private subnet different from the public subnet selected from "Networking" step. The inline error has thrown in the page during cluster creation.

If this is a requirement ,  we should restrict the user with a validation error at the earlier step or update the public subnet list as per the selected private subnet AZ zones.
Note: Cluster creation is successful when the any one of the machine pool AZ belongs to the public subnet AZ.

How reproducible:

 Always

Steps to reproduce:

Pre condition : You have a VPC with 3 public and 3 private subnets distributed across 3 AZ.

1. Launch OCM Staging.
2. Open ROSA wizard and select control plane type as "Hosted"
3. Proceed to next steps by providing all required values in each step.
4. Reach "Machine pools" step and select the VPC.
5. Add a machine pool and select a private subnet values(Belongs to "us-west-2c").
6. Click "Next"  button.
7. Reach to "Networking" step and select a Public subnet id drop-down value (belongs to "us-west-2b")
8. Proceed to next steps by providing all required values in each step.
9. Click "Create cluster" from "Review and create" page.
10. See the behavior. 

Actual results:

Cluster creation fails from wizard as it is reported inline error.

CLUSTERS-MGMT-400: Subnet ID subnet-016664cd481c86d1e does not belong to any of the provided zones. Provide a new subnet ID and try again.Operation ID: 7df6598e-3dfb-40fb-9950-bc908aef6dec

This is because the AZ belongs to private subnet (for machine pool) and AZ belongs to public subnet is different.

Expected results:

Firstly the error message doesn't give a clue what was wrong here. User didn't provide any zones explicitly and it is confusing.

If the requirement is that, anyone of machine pool AZ should belongs to selected public subnet AZ under networking step, We should fix following

1. Filter public subnets based on the machine pool's private subnets. Or
2. Throw a validation at networking step from wizard for above case. 

In case it is not constraint in HCP , then we shouldn't throw any error and cluster creation should be successful.