Add support for tarantool 1.7

With latest tarantool python lib you getting errors like that:
```
  File "ve/lib/python3.5/site-packages/aiotarantool.py", line 38, in <module>
    from tarantool.const import (
ImportError: cannot import name 'ENCODING_DEFAULT'
```

ENCODING_DEFAULT were moved to utils
Also there are small other differences in tarantool python lib that breaks aiotarantool