* Populate push configs when parsing the vagrantfile
* Allow untyped configs to be shipped over GRPC
* In our demo plugin, walk the vagrantfile and snag the config
Example Vagrantfile that works with the demo plugin:
```ruby
Vagrant.configure("2") do |config|
config.push.define "myplugin" do |push|
push.coolkey = "coolvalue"
push.alist = ["so", "many", "items"]
push.ahash = { "hashkey" => "hashvalue" }
end
end
```
This uses the new Push plugin support added to the plugin SDK in https://github.com/hashicorp/vagrant-plugin-sdk/pull/106 to make the following changes:
* The plugin manager on the Go side now registers push plugins
* The the _remote_ plugin manager on the Ruby side now calls over to
the go side to get push plugins
* All the wiring is hooked up such that when a push plugin is replaced
with its remote GRPC-client-wielding equivalent, the messages are
ferried around.
@mitchellh this is a partial revert of 84ae22e. It took me a little bit
to figure out why this broke everything, but then I finally realized it.
84ae22e changes the finalize! function to lookup pushes by strategy
type, but pushes are keyed by push strategy name. In other words, given:
config.push.define("foo", strategy: "bar")
the `push_configs` has will look like:
{ :foo => [:bar, #<PushConfig>] }
This is important, because if we key by strategy, the user cannot
specify the same push strategy more than once:
config.push.define("foo", strategy: "bar")
config.push.define("zip", strategy: "bar")
If we keyed off of the strategy, this would be impossible.
