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.

sdk/go/dockerbuild/internal/pulumiVersion.go

@@ -0,0 +1,11 @@
+// Code generated by pulumi-language-go DO NOT EDIT.
+// *** WARNING: Do not edit by hand unless you're certain you know what you are doing! ***
+
+package internal
+
+import (
+	"github.com/blang/semver"
+)
+
+var SdkVersion semver.Version = semver.Version{}
+var pluginDownloadURL string = ""