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.

Bug: 190222116
Test: atest RemoteProvisionerUnitTests
Change-Id: I917a61da612f21f9a0f783bea5d24270d4e1db42