RUBY-2355 Use server error codes in place of error messages when possible (#2064)

Co-authored-by: Oleg Pudeyev <oleg@bsdpower.com>

Author: p-mongo

lib/mongo/collection.rb

@@ -278,8 +278,12 @@ def drop(opts = {})
                               }).execute(next_primary(nil, session), client: client)
       end
     rescue Error::OperationFailure => ex
-      raise ex unless ex.message =~ /ns not found/
-      false
+      # NamespaceNotFound
+      if ex.code == 26 || ex.code.nil? && ex.message =~ /ns not found/
+        false
+      else
+        raise
+      end
     end
 
     # Find documents in the collection.

lib/mongo/error/operation_failure.rb

@@ -89,7 +89,8 @@ class OperationFailure < Error
       # @since 2.1.1
       # @deprecated
       def retryable?
-        write_retryable? || RETRY_MESSAGES.any?{ |m| message.include?(m) }
+        write_retryable? ||
+        code.nil? && RETRY_MESSAGES.any?{ |m| message.include?(m) }
       end
 
       # Whether the error is a retryable error according to the modern retryable
@@ -102,19 +103,18 @@ def retryable?
       #
       # @since 2.4.2
       def write_retryable?
-        WRITE_RETRY_MESSAGES.any? { |m| message.include?(m) } ||
-        write_retryable_code?
+        write_retryable_code? ||
+        code.nil? && WRITE_RETRY_MESSAGES.any? { |m| message.include?(m) }
       end
 
-      def write_retryable_code?
+      private def write_retryable_code?
         if code
           WRITE_RETRY_ERRORS.any? { |e| e[:code] == code }
         else
           # return false rather than nil
           false
         end
       end
-      private :write_retryable_code?
 
       # Error codes and code names that should result in a failing getMore
       # command on a change stream NOT being resumed.