Fixing the race condition in GenerateRkpKey

This file was written on the assumption that bindService was
synchronous, which it isn't. This change adds a CountDownLatch to force
the class to wait for the binding to finish. If the relevant key
generation service is not present on the system, then this
functionality will just silently be skipped over.

Bug: 190222116
Test: atest RemoteProvisionerUnitTests
Change-Id: Ie34997a08aa743642c66a20c4b756cd47bff4af1
Merged-In: Ie34997a08aa743642c66a20c4b756cd47bff4af1