start-servers operation can start servers when the host is in admin-only mode

If a Host Controler is reloaded or started in admin-only mode, it is possible to start the servers using :start-servers operation. It is problematic when the user reloads the Host Controller without restarting the servers and tries to start the servers afterwards.

By definition, when the host controller is started in admin-only, it will not start any server. Indeed, if the user tries to start a single server using /host=master/server-config=server-one:start an error is correctly reported:

[domain@localhost:9990 /] /host=master/server-config=server-one:start
{
    "outcome" => "failed",
    "failure-description" => "WFLYHC0048: Cannot start servers when the Host Controller running mode is ADMIN_ONLY",
    "rolled-back" => true
}