Automatic merge from submit-queue
add master address into kubeadm join help message and some validations
**What this PR does / why we need it**:
1, add master address into kubeadm join help message. looks like :
>Usage:
> kubeadm join <master address> [flags]
2, when user provides more than one master address, return an error.
3, since `kubeadm join` not only support ip addresses but also host names or domain names, so i delete the word `ip` from error message `must specify master ip address (see --help)`
Signed-off-by: bruceauyeung <ouyang.qinhua@zte.com.cn>
9761442b19