improve verbose logging
improve verbose logging

Summary:
when logging with `--verbose`, adds `(cached)` to flows that hit the
overall flow cache, and a "deferred during speculation" message when a flow is
skipped during speculation.

this helps figure out why the expected sub-flows are missing.

Reviewed By: gabelevi

Differential Revision: D4241345

fbshipit-source-id: 08f48419bb8e6b2b874408152a7a1527541f51ff

gabelevi/flow,TiddoLangerak/flow,mroch/flow,TiddoLangerak/flow,AgentME/flow,ylu1317/flow,samwgoldman/flow,JonathanUsername/flow,ylu1317/flow,samwgoldman/flow,nmote/flow,jamesgpearce/flow,ForbesLindesay/flow,jamesgpearce/flow,nmote/flow,JonathanUsername/flow,claudiopro/flow,mroch/flow,nmote/flow,jamesgpearce/flow,gabro/flow,jamesgpearce/flow,mroch/flow,claudiopro/flow,facebook/flow,JonathanUsername/flow,MichaelDeBoey/flow,fletcherw/flow,nmote/flow,gabelevi/flow,JonathanUsername/flow,nmote/flow,facebook/flow,ForbesLindesay/flow,TiddoLangerak/flow,jamesgpearce/flow,popham/flow,samwgoldman/flow,AgentME/flow,TiddoLangerak/flow,JonathanUsername/flow,gabelevi/flow,facebook/flow,samwgoldman/flow,gabelevi/flow,facebook/flow,ForbesLindesay/flow,mroch/flow,fletcherw/flow,gabro/flow,gabro/flow,jamesgpearce/flow,JonathanUsername/flow,AgentME/flow,MichaelDeBoey/flow,JonathanUsername/flow,claudiopro/flow,popham/flow,gabro/flow,MichaelDeBoey/flow,samwgoldman/flow,nmote/flow,claudiopro/flow,facebook/flow,popham/flow,facebook/flow,MichaelDeBoey/flow,jamesgpearce/flow,fletcherw/flow,ylu1317/flow,nmote/flow,popham/flow,AgentME/flow,ylu1317/flow,gabelevi/flow,AgentME/flow,ylu1317/flow,gabro/flow,mroch/flow,samwgoldman/flow,fletcherw/flow,ForbesLindesay/flow,fletcherw/flow,popham/flow,popham/flow,facebook/flow,mroch/flow,gabelevi/flow,claudiopro/flow,gabelevi/flow,fletcherw/flow,MichaelDeBoey/flow,ForbesLindesay/flow,ForbesLindesay/flow,samwgoldman/flow,mroch/flow,TiddoLangerak/flow,gabro/flow,popham/flow