Refactor `conduit inject` code to make it unit-testable.
Refactor the conduit inject code to make it easier to add unit tests. This work was done by @deebo91 in #365. This is the same PR without the conduit install changes, so that it can land ahead of #365. In particular, this will be used for testing the fix for high-priority bug #366.
Signed-off-by: Dennis Adjei-Baah <dennis@buoyant.io>
Signed-off-by: Brian Smith <brian@briansmith.org>
Brian Smith