Fix hostname conflict in config generator

When the system hostname is the same as a default value in the
config, the _sanitize_default function may replace it incorrectly.
This change checks that the name of the option contains the
substring 'host' to make sure it isn't changing non-hostname
defaults.

Fixes bug 1205411

Change-Id: I93edb2902304c5cd9bfa817b1bccdaec5d807e6c
Merge "Fix hostname conflict in config generator"