Miscellaneous changes before Scheduler 8.x-1.1

For Travis CI testing the tests now fail at Core 8.4 with call to undefined method Drupal::messenger() due to the recent change to use this service (which I guess does not exist in D8.4). We no longer need to test at D8.4 but should add D8.7 instead.

[edit: the commit message is incorrect. Testing at core 8.5 is still done, it is 8.4 which has been dropped now]

Just for fun here's a patch from #2952984-13: Add example drupalci.yml file to un-suppress deprecations to see if we get anyrthing for code test coverage.

The drupalci.yml file is a bigger change and now has it's own issue #3033376: Add drupalci.yml test file to configure d.o. testing

This patch adds @group legacy to our DevelGenerate test, because Devel is using quite a bit of deprecated code which causes test failures on Travis. This patch (and commit) will have no effect on drupal.org testing because deprecation warnings are suppressed and ignored for all contrib, see #2926314: Contrib should run with --suppress-deprecations. Also clone the 2.x branch of Devel not the 1.x branch, as that is more likely where new things will happen.

Tidy up test code:

• Ensure no tests use hard-coded 'page' content type
• tighten up permissions
• do not overwrite $this->adminUser

Core has now released 8.8 as the latest development version and retired 8.5. Our D.O. testing already uses semantic version naming, so our default issue testing has immediately moved on to 8.8. Travis testing at 8.5 can be dropped, and 8.8 added.

According to docs/drupal-ci/customizing-drupalci-testing-for-projects a contrib project's drupalci.yml files should only have the assessment phase , and not the environment and codebase phases.

All Travis builds started failing on 13 Aug with

$ mysql -e "create database $MODULE"
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)
The command "mysql -e "create database $MODULE"" failed and exited with 1 during .

There must have been some tightening up of requirements in the config, as I needed to add

services:
  - mysql

which fixed it. Other modules such as Rules and Typed_data will also need this fix in their .travis.yml file.