Encode vault params in key sync task

Still not sure how we're getting counter_id here, though?

Test: adb shell am instrument -w -e package com.android.server.locksettings.recoverablekeystore com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner
Change-Id: Ic473fff4a19c1d044a6381a1459eca0835a55697