When there is no connection, answer false (#13417)

When building containers, when there is no postgresql instance, this
check to AR::Base.connection is raising an error. We'd like to be able
to continue running `rake assets:precompile` without needing a live db
to check the schema for a table.

Handle connection errors as though they were a table missing.

app/lib/database.rb

@@ -7,7 +7,7 @@ module Database
   # @param table [String] the name of the table to check for
   def self.table_exists?(table)
     ActiveRecord::Base.connection.table_exists?(table)
-  rescue ActiveRecord::NoDatabaseError
+  rescue ActiveRecord::NoDatabaseError, ActiveRecord::ConnectionNotEstablished
     false
   end
 end