Maintenance release

While we're waiting for 0.6.0, this release picks few bug fixes and small improvements from master.

• Use official AWS api libs. Makes flannel work with eu-central-1. Thanks, @kdomanski
• In server mode, notify systemd of readiness once the server is listening. Thanks, @ingvagabund
• Masquerade host to flannel traffic
• Bug fix: close http connection during watch in client mode. Thanks, @jonboulle