sql: Intialize SQL subsystem after config is over

If after recovery first client to invoke SQL differs from
ADMIN, then initialization of SQL subsystem will fail due to
insufficient access rights. Problem is that SQL invokes
create_from_tuple() to fill space_def structure, which in turn
verifies access right.
As far as SQL is a static part of Tarantool, there's no sense
to initialize the system by demand. Change performs data dictionary
initialization upon config completion.
Regression test added as well.

Closes #2483