rename migrations to current date

refs CORE-979

test plan
 - migrations should run

Change-Id: Ib1fe048a10dcd0b3e5b8e54cdfdb71ab0deacaf8
Reviewed-on: https://gerrit.instructure.com/140120
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>
Tested-by: Jenkins

db/migrate/20180207044504_create_lti_resource_links.rb

@@ -20,6 +20,8 @@ class CreateLtiResourceLinks < ActiveRecord::Migration[5.0]
   tag :predeploy
 
   def change
+    return if connection.table_exists? :lti_resource_links
+
     create_table :lti_resource_links do |t|
       t.string :resource_link_id, null: false
       t.timestamps

db/migrate/20180207044934_create_lti_line_items.rb

@@ -20,6 +20,8 @@ class CreateLtiLineItems < ActiveRecord::Migration[5.0]
   tag :predeploy
 
   def change
+    return if connection.table_exists? :lti_line_items
+
     create_table :lti_line_items do |t|
       t.float :score_maximum, null: false
       t.string :label, null: false

db/migrate/20180207045041_create_lti_results.rb

@@ -20,6 +20,8 @@ class CreateLtiResults < ActiveRecord::Migration[5.0]
   tag :predeploy
 
   def change
+    return if connection.table_exists? :lti_results
+
     create_table :lti_results do |t|
       t.float :result_score
       t.float :result_maximum