update code.goole.com/p/go.net to golang.org/x/net

https://groups.google.com/forum/#!topic/golang-nuts/eD8dh3T9yyA
Fix download link in aws/kubecfg documentation

Kubecfg's download link on Darwin and Linux are points to http://storage.googleapis.com/k8s/darwin/kubecfg .
Later one should be changed to http://storage.googleapis.com/k8s/linux/kubecfg .
Merge pull request #2414 from hodduc/fix-aws-doc

Fix download link in aws/kubecfg documentation
Support node label update.
Add more validation for updating node.
more events from kublet
Update development.md

It looks like magic incantation `hack/e2e-test.sh 1 1 1` is not longer supported.
Fix breakage when bringing down cluster.
Merge pull request #2419 from jbeda/fix-teardown

Fix breakage when bringing down cluster.
Merge pull request #2392 from dchen1107/upstream1

Generate container related events from kublet
Fixing systemd service files to point to correct config/executors
Merge pull request #2421 from abhgupta/abhgupta-dev

Fixing systemd service files to point to correct config/executors
Documentation improvements. Fixes #2004, #2115, #2171.
Allow proxy to run on systems with iptables <1.4.11
Merge pull request #2423 from bgrant0607/docfix

Documentation improvements. Fixes #2004, #2115, #2171.
Merge pull request #2397 from ddysher/node-label

Support node label update
Add the 0.5 release.
Add the 0.5-dev tag.
Fix namespace of minion birthcry event.
Merge pull request #2426 from brendandburns/release

Release 0.5