fix sql, bq, storage location exemptions empty list

[xingao267]

Fixes https://github.com/forseti-security/policy-library/issues/369

[xingao267]

Seems like there are test cases for exemption https://github.com/forseti-security/policy-library/tree/master/validator/test/fixtures/sql_location/constraints https://github.com/forseti-security/policy-library/tree/master/validator/test/fixtures/storage_location/constraints https://github.com/forseti-security/policy-library/tree/master/validator/test/fixtures/bq_dataset_location/constraints

[morgante]

None of the existing test cases test what happens when exemptions isn't specified at all. I recommend we add a test case to avoid regression.

[xingao267]

@morgante I modified the allowlist_one test case to not specify the exemptions_list to prevent regression. The empty exemptions_list being specified case is still tested in the allowlist_all case.

[morgante]

Perfect, thanks!