Add a test for exporting the source terms of modules.
This will allow automated scripts to fetch latest terms
Backport save_test_file with a parameter on date_format to have
predictable filenames
closesodoo/odoo#159373
X-original-commit: e7246ea48828746471a2e3a485bee30687eeee80
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>