Include Host string in Request

The Host string provides us with a mechanism for extracting the function
name, which we, in turn, require for things like function-level access
control with OPA.

In Docker Swarm, in particular, the HOSTNAME environment variable (or
manual parsing from /etc/hostname) is insufficient for extracting the
function name, as this simply maps to the container ID.

Resolves #2.

Signed-off-by: Paul Mundt <paul.mundt@adaptant.io>

Author: pmundt

handler.go

@@ -23,6 +23,7 @@ type Request struct {
 	Header      http.Header
 	QueryString string
 	Method      string
+	Host        string
 }
 
 // FunctionHandler used for a serverless Go method invocation