Hostname check with DNS or not

[alexanderkjall]

add an environment variable to control if the hostname check should be performed with a dns resolution or not.

adevinta/vulcan-types#142 needs to be merged and released before this can be evaluated I guess :)

[manelmontilla]

We don't directly access env vars in the logic of the program.
In order to add a config option you need to:

1. Add it to the config file that maps env vars to parameters in the config file
   I think there isn't any section that makes sense to add this new param, so I would add a new section, something like this:

[assets]
dns_hostname_validaton = "$DNS_HOSTNAME_VALIDATION"

2. Map the value in the run script of the container by adding something like this:

export DNS_HOSTNAME_VALIDATION=${DNS_HOSTNAME_VALIDATION:-true}

3. Add the new section in the struct representing the configuration of the api

[alexanderkjall]

Thanks for the review, I updated the branch and tried to apply this feedback.

[manelmontilla]

I added comment with a suggestion to change a little bit the approach.
Apart from that some tests are not parsing, I know is hard to know if the tests are passing or not as the travis builds are not running in the forks. I'll try to add you as collaborator to the vulcan repos, it's not straightforward because someone that is admin of the Adevinta org (which I'm not) must send the invite, so in the future you should be able to create PR's in the repos directly and see the results of the build.
Meanwhile, could you run the tests locally?
To do so, you just need to:

1. Start the persistence layer locally by executing:

cd db
./persistence-start.sh
./flyway-migrate.sh

Note: You will need to have docker installed.

2. Run the go test in the usual way by executing the following from the root of the repo:

go test ./...

[alexanderkjall]

Any update on this one?

[alexanderkjall]

Any update on this one?

[kozmic]

Now that the adevinta/vulcan-types#142 has been merged, could this PR be reviewed and merged @manelmontilla ?

[jesusfcr]

Fixed and merged #317