Fix #7944 add check/test for localhost in ParseHost

Fixes #7944, adds a test case for `addr` set to `localhost:5000`.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
well parse is a package tho so actually I kinda think it should stay as is, so the default values stay in API, or no?