GCE backend, client/server and multi-network modes

New features:

• GCE backend -- analogous to AWS-VPC backend, this manipulates the GCE routes to provide no-encapsulation data plane. Thank you, @MohdAhmad
• Client/Server mode (experimental) -- ability to isolate etcd from nodes by proxying their requests through a server.
• Multi-network mode (experimental) -- run multiple networks at the same time with a single flannel daemon

Bug fixes and improvements:

• Error on start if extraneous args are passed in. Thank you, @jayunit100
• Do not reuse lease if config has changed and is incompatible with the lease.
• AWS-VPC: Auto-detect route table ID if DescribeInstances permission is granted. Thank you, @MohdAhmad
• VXLAN: Statically configure FDB entries. This fixes the first packet dropped issue. Thank you, @titanous and @MohdAhmad

Maintainance release

• host-gw backend: routes did not survive interface going down and up (e.g. cable unplug). Thank you, Huang.
• aws-vpc backend: now supports role based auth in addition to env vars. Thank you, Greg Poirier.
• fixed problem of flannel failing to work with interfaces that have peer addresses defined.
• turn on etcd client logging. This will produce a lot of output but better than no output as it now.

AWS VPC Backend

• Rohan Singh contributed aws-vpc backend (thanks, Rohan). It works by programming the VPC router to forward a subnet to the VM. It allows for elimination of encapsulation overhead while still providing a machine with full subnet.
• Switched over to using master branch of go-etcd

Maintenance release

• flannel will try to recreate VXLAN device every second on startup. Allows for the interface that it's enslaving to come up after flannel (thank you, John W. Linville)
• fix for etcd sockets being leaked (thank you, Lv Lv)

Better IP Masq support and host-gw backend added

1. --ip-masq now works for all backends. Previously it was only
   working properly for UDP backend.
2. Addition of new "host-gw" backend -- thank you, Angus Lees. This
   new backend avoids encapsulation and uses the host's interface as a
   gateway. As a subnet is added or removed, each flannel daemon will
   manipulate the host's routing table to reflect the change. As an
   example, if a host that has an IP 192.168.1.5 adds a flannel subnet
   10.1.8.0/24, the following route would be added to each host:
   10.1.8.0/24 via 192.168.1.5 dev eth0

Addition of VXLAN

• Added VXLAN backend to move encapsulation into the kernel
• Support for multiple etcd endpoints
• Support for TLS between flannel and etcd
• Support for older version of iptables