docker-cli network_mode should default to host if bridge does not exist

Description

There are a few enterprises that do not allow ip_forward or bridge networking. On dockerd the default bridge network can be disabled by setting it to none --bridge=none. When the bridge networking is not present, the cli should use host network by default. The only workaround right now is to pass --net=host every time you run the client but unfortunately there is no way to enforce this globally and there is no solution to make net=host option work with a multi-stage build compose file.

Steps to reproduce the issue:

1. docker run -it alpine ash

Describe the results you received:

WARNING: IPv4 forwarding is disabled. Networking will not work.
/ #

Describe the results you expected:
No warning and using net=host

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker version:

Client:
 Version:      1.13.1-cs9
 API version:  1.27
 Go version:   go1.7.5
 Git commit:   1bc62a2
 Built:        Wed Dec 13 20:56:37 2017
 OS/Arch:      linux/amd64

Server:
 Version:      1.13.1-cs9
 API version:  1.27 (minimum version 1.12)
 Go version:   go1.7.5
 Git commit:   1bc62a2
 Built:        Wed Dec 13 20:56:37 2017
 OS/Arch:      linux/amd64
 Experimental: false

Output of docker info:

Containers: 28
 Running: 1
 Paused: 0
 Stopped: 27
Images: 10
Server Version: 1.13.1-cs9
Storage Driver: overlay
 Backing Filesystem: xfs
 Supports d_type: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 6c463891b1ad274d505ae3bb738e530d1df2b3c7
runc version: 54296cf40ad8143b62dbcaa1d90e520a2136ddfe
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 3.10.0-693.21.1.el7.x86_64
Operating System: Red Hat Enterprise Linux Server 7.4 (Maipo)
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 15.51 GiB
Name: xxx-XXXXX.xxxx.xxx
ID: 2AWA:IH6P:DNWO:GWJD:273C:CEXN:KHYH:SZS7:E4NK:HBOP:W5QA:LBUY
Docker Root Dir: /app/var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Http Proxy: http://XXXXX:XXXX@XXXX.XXXX.XXXX:8080
Https Proxy: http://XXXXX:XXXX@XXXX.XXXX.XXXX:8080
Registry: https://index.docker.io/v1/
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

WARNING: IPv4 forwarding is disabled

Additional environment details (AWS, VirtualBox, physical, etc.):

There is no docker0 network:

docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
f13483c9bbb4        host                host                local
fa5836204847        none                null                local

Start with the docker run network-option handling and examine how the CLI behaves when the bridge network is absent. Reproduce the issue with only host and none networks, then verify that docker run -it alpine ash selects host networking without the IPv4-forwarding warning.