Housekeeping (#8)

* Rename the provider to dockerbuild.
* Add Makefile targets required by CI.
* Add per-language test targets compatible with CI.
* Fix broken example yaml.
* Add gitignore exclusions to fix SDK generation in CI.
* Fix lint errors.
* Vendor pulumi CLI via `tools.go` instead of `.pulumi`.
* Consolidate `go.mod`s into one file, with a minimal `go.mod` for the
Go SDK.
* Add codecov.

.gitignore

@@ -5,12 +5,16 @@
 **/.vs
 **/.idea
 **/.ionide
-.pulumi
+*.swp
 Pulumi.*.yaml
 yarn.lock
 ci-scripts
-/nuget/
-provider/**/schema-embed.json
+nuget/
+coverage.txt
 
 
+sdk/dotnet/version.txt
+sdk/java/.gradle
+sdk/java/build/
+sdk/java/build.gradle
 sdk/python/venv