Automatic Renewal

[Greek64]

The le-companion is renewing the Certificates when they are valid for less than 30 days.
This is currently achieved by simply not setting the --valid_min option of the simp_le client (i.e. using the default setting).

Even if this is documented in the Manifesto of simp_le (https://github.com/zenhack/simp_le), we are relying on a default value, about something we explicitly want to have. In others words it would make more sense to set this explicitly.

Actually we could add another environmental variable (e.g LETSENCRYPT_MIN_VALID), so that every user can customize this to their liking (of course with the according sanity checks, to prevent a min-validity larger that LE will give)

And also, as it currently stands, the auto renewal process is not even tested by the test units (only the default_cert unit tests the renewal of the default certificate).
Adding a variable would allow to "spoof" the validity check (by giving a higher min validity than the current certs have), in order to test the auto renewal feature.

If interested, I could make a PR for this (including new test unit for auto renewal test)

[buchdag]

And also, as it currently stands, the auto renewal process is not even tested by the test units (only the default_cert unit tests the renewal of the default certificate).
Adding a variable would allow to "spoof" the validity check (by giving a higher min validity than the current certs have), in order to test the auto renewal feature.

In fact this is already more or less what the force_renew script does, and this one is tested.

Anyway the feature seems sound to me, feel free to submit a PR 👍