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/java/settings.gradle

@@ -0,0 +1,14 @@
+// *** WARNING: this file was generated by pulumi-java-gen. ***
+// *** Do not edit by hand unless you're certain you know what you are doing! ***
+
+pluginManagement {
+  repositories {
+    maven { // The google mirror is less flaky than mavenCentral()
+      url("https://maven-central.storage-download.googleapis.com/maven2/")
+    }
+    gradlePluginPortal()
+  }
+}
+
+rootProject.name = "com.pulumi.dockerbuild"
+include("lib")