Make test is effectively an in-tree build

[SeanTAllen]

So, in-tree builds are bad. We try to avoid them with all our makefiles. Everything goes into build/ however, we have tests that use the testdata in corral/test/test-data which in turn as lock.json files created there in the tree.

I have a PR open that adds a .gitignore to testdata to prevent lock.json files from being added. This is however, a workaround. Really as part of testing, the testdata should be copied into build and used from there.

How exactly we do this PATH wise is unclear. We don't have a good mechanism for this.

Additionally we need to make sure the makefile will correctly handle the dependency such that if any changes are made in corral/test/testdata that it will be updated in build.