Adapt one of the omprog tests to the latest improvements in the
testbench framework, for consistency with other similar tests. The test
behaviour has not changed.
Add some temporary files created by the testbench to gitignore file.
Also now permit interactivly running tests without explicitly setting
$srcdir. This now works if we are inside ./tests and fails, as before,
when we are in a different directory.
Detected by shellcheck via CodeFactor.io
