Bugfix and DRY out code

[Peter-Darton-i2]

There's a few bugs w.r.t. handling things "not in the base folder" or "not in an absolute path".

Orb bugs fixed:

• the parallel_test job doesn't cope at all if app_src_directory is set; it ignores it when running maven
• both test and parallel_test jobs use the process_test_results command which wasn't told app_src_directory at all, so the default target/... would no longer work if app_src_directory was set
• the test-splitting logic now copes (no longer crashes out) if we're missing surefire and/or failsafe tests (the sample_app only has surefire)

CI issues:

• The repo had two maven "sample_app" folders, both containing unwanted files, doing largely the same thing with varying levels of success. I've taken the best of both.
• ... and their "unit tests" have been expanded on in order to allow for better testing of the parallel_test's test-splitting code.
• Lots of files were marked as executable when they weren't executable.
• All the scripts were marked as not executable when they are executable scripts.
• The empty /.github/.gitignore file has been removed
• The sample_app now has a .gitignore file preventing the target folder being re-added to git
• The run-parallel-tests.sh script's parallel-specific code has been merged into the run-tests.sh script so now we only need the latter.