iproto: add missing IPROTO feature flags to greeting negotiation

The flags of functions IPROTO_FEATURE_IS_SYNC and IPROTO_FEATURE_INSERT_ARROW protocol function flags were added in the welcome, fixed tests that test for flags by adding a byte sequence.

Added #466

Author: babyTsakhes

CHANGELOG.md

@@ -36,6 +36,8 @@ flag handling, and fixes watcher panic.
   Now you can check this error with `errors.Is(err, tarantool.ErrConcurrentSchemaUpdate)`.
 - Implemented support for `IPROTO_IS_SYNC` flag in stream transactions,
   added `IsSync(bool)` method for `BeginRequest`/`CommitRequest` (#447).
+- Added missing IPROTO feature flags to greeting negotiation (iproto.IPROTO_FEATURE_IS_SYNC,
+iproto.IPROTO_FEATURE_INSERT_ARROW) and fixed tests that test for flags by adding a byte sequence.
 
 ### Fixed