Add table tests for importers

[carolynvs]

It would help when maintaining importers to have their tests operate on the same testdata. Each row in the table would be the tool's config (e.g. glide.yaml/lock), but the output for each will be the same Gopkg.toml/lock. If a tool has edge cases beyond the "lowest common denominator" between the tools, then it should be validated in a separate unit test.

For example, the test cases for glide and godep are very sim liar but have slight changes

[sebdah]

FYI, I've started looking at this. Will submit a WIP PR in the next day or so to confirm that my approach is ✅.

[sebdah]

Have added the above referenced PR to introduce table based tests for the godep and glide importers.