prci_definitions: update vagrant memory topology requirements
    
    Memory requirements for master and replica have been increased
    due to OOM issues. This PR updates prci_definitions accordingly.
    
    This PR also roll-back ipaserver mem reqs to the previous value
    since the WebUI tests were split into different blocks.
    
    Fixes https://pagure.io/freeipa/issue/7777
    
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>