Code review comment for ~aym-frikha/charm-mongodb:branch_1946810

> I note that not every reference to default_mongodb_* is prefixed with a
> conditional for is_percona_source(). Is that deliberate because it's not
> needed in some cases, or is it maybe easier to have is_percona_source used in
> some initial variable setup outside of the remaining functions, so that we
> have the `# Global variables ` section set up with generic names for paths
> that are adjusted according to the package source?

For default_mongodb_config and default_mongodb_pid_file, every reference is prefixed with a conditional for is_percona_source() to be adjusted based on the package source, only the default_mongodb_init_config variable is not prefixed since it's not necessary in this situation.
In my opinion, the charm code needs a big redesign (split into classes and scripts) to have simpler review process and understandable code.

> Regards the CI failures, I'm running a test to see if it's due to Xenial and
> various Python package changes that have recently meant for some other charms
> that we've had to remove Xenial support.