Fix tests.txt parsing for brillo_tests

With the format change to tests.txt to support sending flags to
the tests, update the brillo_tests packaging regex to match.

Bug: 27818067
Test: `m -j40 dist brillo_tests` creates test zip, contains the tests.
Change-Id: I351e0643504edc5790b4f71240642c3739b7c84a
1 file changed