Threadpool can now be configured/joined if needed with
configureRpcThreadpool() / joinRpcThreadpool().
Bug: 31226656
Test: mma
Change-Id: I0d7d9924cc8c8851cc2b61ebdae906204909890e
This is only for hals which are currently only in master. Separate
commit for hals currently in AOSP.
Test: pass
Change-Id: I0b1a09798c49f4f0141f36a322c4749e47eded03