scheduler: Make 'https://' optional in 'server' config field.

scheduler/appengine/task/buildbucket/buildbucket_test.go

Index: scheduler/appengine/task/buildbucket/buildbucket_test.go
diff --git a/scheduler/appengine/task/buildbucket/buildbucket_test.go b/scheduler/appengine/task/buildbucket/buildbucket_test.go
index 1e2b847baa16081d51214cd70025bd34d726f576..4a366eb58fce3bbabab7ed78c48f6eadc25ed191 100644
--- a/scheduler/appengine/task/buildbucket/buildbucket_test.go
+++ b/scheduler/appengine/task/buildbucket/buildbucket_test.go
@@ -46,7 +46,7 @@ func TestValidateProtoMessage(t *testing.T) {
 
 	Convey("ValidateProtoMessage passes good minimal msg", t, func() {
 		So(tm.ValidateProtoMessage(&messages.BuildbucketTask{
-			Server:  "https://blah.com",
+			Server:  "blah.com",
 			Bucket:  "bucket",
 			Builder: "builder",
 		}), ShouldBeNil)
@@ -70,7 +70,7 @@ func TestValidateProtoMessage(t *testing.T) {
 		}
 		So(call(""), ShouldErrLike, "field 'server' is required")
 		So(call("%%%%"), ShouldErrLike, "invalid URL")
-		So(call("/abc"), ShouldErrLike, "not an absolute url")
+		So(call("/abc"), ShouldErrLike, "not a host root url")
 		So(call("https://host/not-root"), ShouldErrLike, "not a host root url")
 	})