"Create Cluster" present when user has Reader role

[rsmitty]

Nit:

Testing the SAML -> Omni roles with powerflex. Max assigned me to a group that gives me Reader role upon login. This works as expected. However, on the "Clusters" view, the "Create Cluster" button is still present and appears as if it would allow you to at least go through the process of creating a cluster (though it might fail once submitted). We should consider hiding this button.