Cocaine-framework-python: fixed tests.

* some tests have been broken after renaming
Fixed data loss bug on synchronous chain usage.

* if you created multiple chains via service invocation and lately invoke `get` method to get chain result synchronously, other chains are also activated (cause there is only thread local event loop). This led to the data loss. Now results are stored in chain object.
* errors are transmitted to `ChainItem.callback` method even if there is no next handler
* pending results are saved in `ChainItem` objects to prevent data loss on synchronous usage
* test has been written
Fixed extra memory consumption.
Merge branch 'master' of github.com:cocaine/cocaine-framework-python