Found and eliminated hidden cyclic referencing.

Connect deferred will no longer be kept alive after connection establishing. Previously it kept tracking callback function, which pointed (via ~5 references) to itself.
As a result, socket fd's leaked extremely fast if services connected asynchronously after its creation. Moreover service object itself never was destroyed by GC.
Merge branch 'release' of github.com:cocaine/cocaine-framework-python into release
Merge branch 'release'