virsh: Track when create pkttyagent
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1374126
    
    Due to how the processing for authentication using polkit works, the
    virshConnect code must first "attempt" an virConnectOpenAuth and then
    check for a "special" return error code VIR_ERR_AUTH_UNAVAILABLE in
    order to attempt to "retry" the authentication after performing a creation
    of a pkttyagent to handle the challenge/response for the client.
    
    However, if pkttyagent creation is not possible for the authentication
    being attempted (such as perhaps a "qemu+ssh://someuser@localhost/system"),
    then the same failure pattern would be returned and another attempt to
    create a pkttyagent would be done. This would continue "forever" until
    someone forced quit (e.g. ctrl-c) from virsh as the 'authfail' was not
    incremented when creating the pkttyagent.
    
    So add a 'agentCreated' boolean to track if we've attempted to create the
    agent at least once and force a failure if that creation returned the same
    error pattern.
    
    This resolves a possible never ending loop and will generate an error:
    
    error: failed to connect to the hypervisor
    error: authentication unavailable: no polkit agent available to authenticate action 'org.libvirt.unix.manage'
    
    NB: If the authentication was for a sufficiently privileged client, such as
    qemu+ssh://root@localhost/system, then the remoteDispatchAuthList "allows"
    the authentication to use libvirt since @callerUid would be 0.