Simplify how modules extend regression tests.

[aaronweeden]

Description

This PR reduces duplicated code to simplify how the modules (xdmod-supremm, xdmod-ondemand) extend the regression tests.

There are corresponding PRs for ubccr/xdmod-supremm#371 and ubccr/xdmod-ondemand#39.

This PR also adds OnDemand to the usage message in tests/ci/runtest-include.sh since new OnDemand regression tests are being added in ubccr/xdmod-ondemand#39.

The duplicated code is reduced as follows:

• Rather than the modules overriding the method MetricExplorerChartsTest.php::filterTestsProvider() by copy-pasting that method and changing the values of $data_file and $baseConfig, this PR changes the code to:
  • determine the location of $data_file relative to the file that defines the class whose instance is calling filterTestsProvider(), and
  • obtain $baseConfig from a new static method called getFilterTestBaseConfig(), which the module overrides.
• Duplicated code in the classes UsageExplorer{Cloud|Job|Resourcespecifications|Storage}Test is abstracted into an abstract class aUsageExplorerTest.
• Rather than the modules redefining their own runtests.sh script, they simply source the main runtests.sh script.

Motivation and Context

Code cleanup.

Tests performed

I made sure the same number of regressions tests ran and passed on this PR as the current head of xdmod11.0.

TODO: test other modules in Docker

Checklist:

• The pull request description is suitable for a Changelog entry
• The milestone is set correctly on the pull request
• The appropriate labels have been added to the pull request