Check /etc/resolv.conf every time for 127.* content

Currently if you start the docker -d on a system with 127.0.0.1 in /etc/resolv.conf
It will set the default dns to 8.8.8.8 8.8.4.4 permanently.

This causes a problem at boot on Fedora machines where NetworkManager has not
populated /etc/resolv.conf before docker gets started.

This fix checks /etc/resolv.conf on every docker run. And only populates
daemon.config.Dns  if the user specified it on the command line.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Test for check /etc/resolv.conf on every docker run for 127.* content.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
cleanup resolve.conf code

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
Merge pull request #8457 from jfrazelle/pr_8455

Check /etc/resolv.conf every time for 127.* content