testable-artifact-builder should provide an option to write packages to devDependencies

[thompsnm]

Background:
When testable-artifact-builder runs installSnapshots it adds the test dependencies to the dependencies object in the package.json so that npm won't throw errors about dependency mismatches. However, some projects don't want any modules in the dependencies object. For instance, if a projects is bundled using webpack instead of npm and then is published as a resulting dist then adding modules to the dependencies object will just cause extra installs to occur downstream for no reason. In that case it would be nice if testable-artifact-builder was parameterized so that the user could tell it to add the dependencies to the devDependencies object instead. That would prevent version mismatch errors, but downstream projects wouldn't have to install extraneous dependencies.

AC:

• Add a --install-as-dev option to the installSnapshots command in testable-artifact-builder that tells it to install test dependencies to the devDependencies object.