With the draft to support both gob and protobuf as serialisation formats
for Packer, along with the SDK changes that propel them, we add a series
of tests that make sure the logic that picks which protocol is solid and
functional.
These tests rely on building several versions of the tester plugin, with
and without protobuf support, to then install them in the tests as
needed to test the logic of Packer using packer build with them, and
templates that require multiple plugins.
Having only one test suite for the whole of Packer makes it harder to
segregate between test types, and makes for a longer runtime as no tests
run in parallel by default.
This commit splits the packer_test suite into several components in
order to make extension easier.
First we have `lib`: this package embeds the core for running Packer
test suites. This ships facilities to build your own test suite for
Packer core, and exposes convenience methods and structures for building
plugins, packer core, and use it to run a test suite in a temporary
directory.
Then we have two separate test suites: one for plugins, and one for core
itself, the latter of which does not depend on plugins being compiled at
all.
This sets the stage for more specialised test suites in the future, each
of which can run in parallel on different parts of the code.
