Set hard-coded unix sockets for iproto connections at core = app.
Added its option in *-tap/suites.ini files and fixed test for it.
Fix helped to handle the problem with 'Address already in use' error.
Check the previous commit that set the use of sockets:

60f84cbf ('test: use unix sockets for iproto connections')

Test sql-tap/gh-4077-iproto-execute-no-bind.test.lua removed from
fragiled list.

Closes #4459