fix gradebook_history to ignore placeholder submissions

Expands the not_placeholder definition to include items where the
submission.workflow_state is graded and adds not_placeholder to
submission calls in SubmissionList and in gradebook_history in the
GradebooksController

fixes CNVS-37503

test plan:
 - Have a new course with 5 students
 - Create 5 assignments assigned to all students with a due date
 - In the rails console execute:
    - Setting.set('gradebook_history_submission_count_threshold', 20)
 - Grade one or two assignments for one student
 - Visit gradebook history, ensure it loads and shows the proper data

Change-Id: If44b4be519c4806d060e15b4506c003555839508
Reviewed-on: https://gerrit.instructure.com/116058
Reviewed-by: Derek Bender <djbender@instructure.com>
Reviewed-by: Neil Gupta <ngupta@instructure.com>
Tested-by: Jenkins
QA-Review: Anju Reddy <areddy@instructure.com>
Product-Review: Keith T. Garner <kgarner@instructure.com>

app/controllers/gradebooks_controller.rb

@@ -430,7 +430,7 @@ class GradebooksController < ApplicationController
       # in large courses in a performant manner. Until that happens, we're
       # disabling it over a certain threshold.
       #
-      submissions_count = @context.submissions.count
+      submissions_count = @context.submissions.not_placeholder.count
       submissions_limit = Setting.get('gradebook_history_submission_count_threshold', '0').to_i
       if submissions_limit == 0 || submissions_count <= submissions_limit
         # TODO this whole thing could go a LOT faster if you just got ALL the versions of ALL the submissions in this course then did a ruby sort_by day then grader

app/models/submission.rb

@@ -1685,7 +1685,7 @@ class Submission < ActiveRecord::Base
   scope :having_submission, -> { where("submissions.submission_type IS NOT NULL") }
   scope :without_submission, -> { where(submission_type: nil, workflow_state: "unsubmitted") }
   scope :not_placeholder, -> {
-    where("submissions.submission_type IS NOT NULL or submissions.excused or submissions.score IS NOT NULL")
+    where("submissions.submission_type IS NOT NULL or submissions.excused or submissions.score IS NOT NULL or submissions.workflow_state = 'graded'")
   }
 
   scope :include_user, -> { preload(:user) }

lib/submission_list.rb

@@ -203,7 +203,7 @@ class SubmissionList
 
     # A hash of the current grades of each submission, keyed by submission.id
     def current_grade_map
-      @current_grade_map ||= self.course.submissions.inject({}) do |hash, submission|
+      @current_grade_map ||= self.course.submissions.not_placeholder.inject({}) do |hash, submission|
         grader = if submission.grader_id.present?
           self.grader_map[submission.grader_id].try(:name)
         end
@@ -295,7 +295,7 @@ class SubmissionList
 
     # A list of all versions in YAML format
     def yaml_list
-      @yaml_list ||= self.course.submissions.preload(:versions).map do |s|
+      @yaml_list ||= self.course.submissions.not_placeholder.preload(:versions).map do |s|
         s.versions.map { |v| v.yaml }
       end.flatten
     end