Refactor vendor_passthru to use conductor async workers

To acheive sync validation + async vendor action we used two rpc calls.
Currently we have async workers mechanism in conductor so this patch
changes vendor_passthru flow to:
rpc CALL -> validate -> spawn worker -> return driver info.

Also this patch moves vendor_passthru exclusive lock creation to
conductor level to have common lock for the whole method and prevent
races.

Change-Id: I9b0173841398d72b1818e986caf3d9a486cd205e
Merge "Refactor vendor_passthru to use conductor async workers"