Support new _index system space format

[Totktonada]

After tarantool-1.7.5-153-g1651fc9be the new _index format was introduced. We should support it to fetch a schema from a tarantool-1.7.5.153+ instance.

When an index parts do not use parameters except name and type the index info is stored in the old format in _index system space and the connector works. When an index part uses is_nullable or collation parameter, the the new format will be used and the connector will not work (will fail on schema fetching as in #127).

All system spaces except _func uses the old _index format. The _func system space has a secondary index with unicode_ci collation on several tarantool versions:

• Neither of 2.1 and below.
• All 2.2.* since 2.2.0-558-g200a492aa (inclusive).
• All 2.3.* until 2.3.0-259-gf88f9731a (exclusive).
• Neither of 2.4.*.

However if a user defines a space with an index with is_nullable or collation index part parameters, then, again, the schema fetching will not work.