Attach EventBase to proxy from proxy's thread
Attach EventBase to proxy from proxy's thread

Summary: For cycles API, we the code that attaches the eventbase to the proxy,
to be executed by the proxy's thread.

Test Plan: Unit tests, manual tests.

Reviewed By: @alikhtarov

Differential Revision: D2027696
facebook/mcrouter,is00hcw/mcrouter,tempbottle/mcrouter,yqzhang/mcrouter,zhlong73/mcrouter,is00hcw/mcrouter,leitao/mcrouter,synecdoche/mcrouter,yqzhang/mcrouter,reddit/mcrouter,tempbottle/mcrouter,synecdoche/mcrouter,zhlong73/mcrouter,evertrue/mcrouter,facebook/mcrouter,easyfmxu/mcrouter,evertrue/mcrouter,facebook/mcrouter,glensc/mcrouter,evertrue/mcrouter,evertrue/mcrouter,reddit/mcrouter,zhlong73/mcrouter,tempbottle/mcrouter,glensc/mcrouter,is00hcw/mcrouter,facebook/mcrouter,easyfmxu/mcrouter,leitao/mcrouter,synecdoche/mcrouter,yqzhang/mcrouter,tempbottle/mcrouter,is00hcw/mcrouter,nvaller/mcrouter,glensc/mcrouter,nvaller/mcrouter,reddit/mcrouter,synecdoche/mcrouter,zhlong73/mcrouter,nvaller/mcrouter,easyfmxu/mcrouter,leitao/mcrouter,glensc/mcrouter,yqzhang/mcrouter,reddit/mcrouter,easyfmxu/mcrouter,leitao/mcrouter,nvaller/mcrouter