server install: fix KRA agent PEM file not being created
    
    In commit 822e1bc82af3a6c1556546c4fbe96eeafad45762 the call to create the
    KRA agent PEM file was accidentally removed from the server installer.
    
    Call into the KRA installer from the server installer to create the file
    again.
    
    https://fedorahosted.org/freeipa/ticket/6392
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>