/reviewed-on nexedi/slapos.toolbox!78

Fixed check_surykatka_json for http-only sites

Enhancements:

 * implement ignore-code
 * cover http_code
 * cover timeout
 * implement verify
 * correctly cover ca-cert-file
 * use SLAPOS_TEST_IPV4

First start of promise migration to new python promises format. Promises migrated here are
used in caddy-frontend and monitor stack.

It can exclude directories from the hash computation, which may
be handy for more than one software release.
Its first application will be to exclude logrotated logs from the signature
file, and the zodb backup, as they integrate their own integrity mechanisme

Rewrite the [runner-exporter bash script](https://lab.nexedi.com/nexedi/slapos/blob/2a01586bfe17f46e2ef26ec6e45bef692435ed28/software/slaprunner/template/runner-export.sh.jinja2) in python.

Also parametarize the signature function to not use only sha256sum which can create issues on some systems. This should be a separated commit, but that shouldn't be a blocker.

Write unit tests for the main functions of this exporter script. As every trick in the original bash script were not obvious / understood / found by me, I may have missed some.

/reviewed-on nexedi/slapos.toolbox!44

This is the promise that will be used for the backupserver software release. It is working as is (with some needed changes in backupserver software release of course) but I may add more features.

I'd like to have a first review of my code.

/reviewed-on nexedi/slapos.toolbox!43