Update container resolv.conf when host network changes /etc/resolv.conf

Addresses #9202 

Only modifies non-running containers resolv.conf bind mount, and only if
the container user has not modified the original resolv.conf at
container start time (so we don't overwrite manual/automated changes
within the container runtime).

**Notes:**
- This code won't build properly until #9634 is merged.  (You can cherry pick 9bc66d04931856da2f3ca7447b2404d37d84a667 if you would like to test this code)
- Given we (@crosbymichael and I discussed) stepped back from updating running containers I would like to add some kind of hook into this code on *start* or *stop* to catch the containers that are running when the host change happened--this would allow containers to be "bounced" to pick up resolv.conf updates

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
Why you use `var` here? I think it is better just use `:=` to not confuse reader.