Add builder manager support (#308)

This change orchestrates function builds.

Environments (in v2) define a builder image, just like they do a runtime image. The builder image contains a build script that's invoked with source and deployment paths (as env vars).

The buildermgr watches for environments with build images defined, and creates build deployments and services.

Functions can define source and deployment. Buildermgr watches for functions with source code (and build status == pending) and invokes the environment's builder when appropriate. It captures logs from the build and sets the build status (success/failure) and build lots into the PackageStatus.

types.go

@@ -65,9 +65,10 @@ type (
 	BuildStatus string
 
 	PackageSpec struct {
-		Environment EnvironmentReference `json:"environment"`
-		Source      Archive              `json:"source"`
-		Deployment  Archive              `json:"deployment"`
+		Environment  EnvironmentReference `json:"environment"`
+		Source       Archive              `json:"source"`
+		Deployment   Archive              `json:"deployment"`
+		BuildCommand string               `json:"buildcmd"`
 		// In the future, we can have a debug build here too
 	}
 	PackageStatus struct {
@@ -220,11 +221,11 @@ type (
 		// env-specific. Optional.
 		FilePath string `json:"filepath"`
 
-		// Entrypoint has an environment-specific meaning;
+		// FunctionName has an environment-specific meaning;
 		// usually, it defines a function within a module
 		// containing multiple functions. Optional; default is
 		// environment-specific.
-		EntryPoint string `json:"entrypoint"`
+		FunctionName string `json:"functionName"`
 
 		// URL to expose this function at. Optional; defaults
 		// to "/".