Cleanup ParseHost

Current implementation is comingling things that ought not be together.
There are _some_ similarities between parsing for the different proto
types, but they are more different than alike, making the code extremely
difficult to reason about.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Merge pull request #9030 from cpuguy83/cleanup_host_parser

Cleanup ParseHost