Improvements:
 * use real dict in the test
 * merge test cases
 * increase test coverage
 * minimize and improve messages
 * use error state instead of error list
 * always shall full diff during test failure to ease debugging
 * fix ssl_certificate missing information
 * avoid cluttering code with test time

See merge request !113

Also add a "Requires-Python" information so that dropping python2
support will be easier in the future. See https://packaging.python.org/en/latest/guides/dropping-older-python-versions/

Note that this promise is only available in Python3.

We are going to delete instance-gitlab-test.cfg.in from slapos repo,
which is dedicated to testing, now we are going to test the file
which is used in production, aka instance-gitlab.cfg, as a part of
theia resiliency test

webrunner is replaced by Theia

See merge request !108

See merge request nexedi/slapos.toolbox!105

slapos/promise/plugin/util.py: Modified getJsonLogLatestTimestamp() to use current_time instead of latest_timestamp

promise: Merged check_free_disk_space and monitor_partition_space from @lisa.casino & @@xavier_thompson

collect data in slapos.core are stored into db with gmtime which was
different from utc used by monitor.

urlopen(url).read() returns bytes, this fixes:

      File "slapos.toolbox-repository/slapos/resiliencytest/suites/resiliencytestsuite.py", line 162, in _waitForCloneToBeReadyForTakeover
        while "<b>Importer script(s) of backup in progress:</b> True" in takeover_page_content:
    TypeError: a bytes-like object is required, not 'str'

errors with KVM resilience tests

Improved error text for misnamed InvalidSchema and MissingSchema exceptions.

https://github.com/psf/requests/blob/v2.27.0/HISTORY.md#2270-2022-01-03

See merge request nexedi/slapos.toolbox!102

The test doesn't care about the instance state, just wants an
 arbitrary instance title.

This promise relates to resources local on the partition, which are files, and
they shall be available fast, thus make it failing immediately in case of
failure.

See merge request !100

If there is no url parameter the promise fails, so simply switch to empty.