Automatic merge from submit-queue

[kubelet] Auto-discover node IP if neither cloud provider exists and IP is not explicitly specified

One example where the earlier implementation failed is when running kubelet on CoreOS (bare-metal), where the nameserver is set to `8.8.8.8`. kubelet tries to lookup the node name agains Google DNS, which obviously fails. The kubelet won't recover after that.

The workaround hsa been to set `--hostname-override` to an IP address, but it's quite annoying to try to make a multi-distro way of getting the IP in bash for example. This way is much cleaner.

Refactored the function a little bit at the same time

@vishh @yujuhong @resouer @Random-Liu