Ensure unique identifiers in fabricated objects in tests (#3173)

spec/fabricators/account_domain_block_fabricator.rb

 Fabricator(:account_domain_block) do
-  account_id 1
-  domain     "MyString"
+  account
+  domain 'example.com'
 end

spec/fabricators/account_fabricator.rb

 Fabricator(:account) do
-  username { Faker::Internet.user_name(nil, %w(_)) }
+  username { sequence(:username) { |i| "#{Faker::Internet.user_name(nil, %w(_))}#{i}" } }
   last_webfingered_at { Time.now.utc }
 end

spec/fabricators/preview_card_fabricator.rb

 Fabricator(:preview_card) do
-  status_id 1
-  url       "MyString"
-  html      "MyText"
+  status
+  url 'http://example.com'
 end

spec/fabricators/tag_fabricator.rb

 Fabricator(:tag) do
-  name "MyString"
+  name { sequence(:hashtag) { |i| "#{Faker::Lorem.word}#{i}" } }
 end

spec/fabricators/user_fabricator.rb

 Fabricator(:user) do
   account
-  email        { Faker::Internet.email }
+  email        { sequence(:email) { |i| "#{i}#{Faker::Internet.email}" } }
   password     "123456789"
   confirmed_at { Time.now }
 end