New function get_total_content_size() is introduced in the stored_file
class. The puprose of this function is to calculate and return the
total size (in bytes) of the content of an archive file.

Merge branch 'install_37_STABLE' of https://git.in.moodle.com/amosbot/moodle-install into MOODLE_37_STABLE

If a scheduled task which uses a 'R' field is picked, then the reset of
updated task times will not necessarily be correctly determined as the
randomisation is picked during reset.

This can lead to some random test failures.

Actively specifying a test which does not make use of the 'R' random
field time addresses this issue.

The result of the final command `script` phase determines the build
result.

The cleanup belongs in the `after_script` phase.

Both ldap or the DB can return information in a non-consistent
ordering leading to events to be generated in different order.

And current tests are, right now, assuming a given order.

Note this is a rare random, but it's happening, so better
fix it, see the issue for some more details.

So we just do the tests ordering immune, verifying that all the
expected events have been triggered and done. Irrespectively of their order.

- mysql requirement up to 5.7
- postgres requirement up to 9.6

This is a direct copy of the 3.9 branch to have
changes under control easier for next commits.

Merge branch 'install_37_STABLE' of https://git.in.moodle.com/amosbot/moodle-install into MOODLE_37_STABLE