Refactor and fix register interface when bridge does not exist

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge branch 'fix-register-nobridge' of https://github.com/crosbymichael/docker into crosbymichael-fix-register-nobridge
Update tests to have custom routes

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Update README.md
Docker-DCO-1.1-Signed-off-by: Simon Taranto <simon.taranto@gmail.com> (github: srt32)
Merge pull request #3771 from srt32/patch-1

Update README.md typo
Merge pull request #3756 from crosbymichael/fix-register-nobridge

Refactor and fix register interface when bridge does not exist