Support for starting transaction in another thread

[voipp]

Hi, Igniters! This is a subtask for "distributed transaction of non-single
coordinator" task.
Will appreciate your thoughts on it.
ticket : https://issues.apache.org/jira/browse/IGNITE-4887
and a commit :
https://github.com/voipp/ignite/commit/aa3487bd9c203394f534c605f84e06436b638e5c
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*Best Regards,*

*Kuznetsov Aleksey*