bndlib tests: Not all locales use , as thousands separator

Use grouping separator from default locale in expected value.

Fixes https://github.com/bndtools/bnd/issues/643

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
Merge pull request #644 from bjhargrave/issue643

bndlib tests: Not all locales use , as thousands separator