Previously, hosts were de-duplicated and normalized when starting
the API server (in `loadListeners()`), which meant that errors could
occur in that step (but not detected when using `dockerd --validate`),
as well as the list of hosts in the config not matching what would
actually be used (i.e., if duplicates were present).
This patch extracts the de-duplicating to a separate function, and
executes it as part of loading the daemon configuration, so that we
can fail early.
Moving this code also showed that some of this validation depended
on `newAPIServerConfig()` modifying the configuration (adding an
empty host if none was set) in order to have the parsing set a
default. This code was moved elsewhere, but a TODO comment added
as this logic is somewhat sketchy.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
57c20c1b79