add root account id to instfs preflight json

closes RECNVS-38

test plan: none
(this commit will be tested as a part of RECNVS-39)

Change-Id: I39c39974c8f9553af5057e159c419cd84397caf8
Reviewed-on: https://gerrit.instructure.com/136940
Tested-by: Jenkins
Reviewed-by: Jacob Fugal <jacob@instructure.com>
QA-Review: Collin Parrish <cparrish@instructure.com>
Product-Review: Andrew Huff <ahuff@instructure.com>

lib/inst_fs.rb

@@ -55,6 +55,7 @@ module InstFS
         context_id: context.global_id.to_s,
         user_id: user.global_id.to_s,
         folder_id: folder && folder.global_id.to_s,
+        root_account_id: context.account.root_account.global_id.to_s,
         quota_exempt: !!quota_exempt,
         on_duplicate: on_duplicate)
 

spec/lib/inst_fs_spec.rb

@@ -110,7 +110,7 @@ describe InstFS do
   end
 
   context "upload_preflight_json" do
-    let(:context) { instance_double("Course", id: 1, global_id: 101) }
+    let(:context) { instance_double("Course", id: 1, global_id: 101, account: Account.default) }
     let(:user) { instance_double("User", id: 2, global_id: 102) }
     let(:folder) { instance_double("Folder", id: 3, global_id: 103) }
     let(:filename) { 'test.txt' }
@@ -181,6 +181,10 @@ describe InstFS do
           expect(capture_params['folder_id']).to eq folder.global_id.to_s
         end
 
+        it "include the root_account_id" do
+          expect(capture_params['root_account_id']).to eq context.account.root_account.global_id.to_s
+        end
+
         it "include the quota_exempt flag" do
           expect(capture_params['quota_exempt']).to eq quota_exempt
         end