Fix bug where PlatformKeyManager did not save generation ID

This caused a new platform key to be repeatedly generated. Also fix an issue
where you had to have the RECOVER_KEYSTORE permission to check the status of
your own keys. This does not make sense.

Test: adb shell am instrument -w -e package com.android.server.locksettings.recoverablekeystore com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner
Change-Id: I51aa4e1fe1a96b79bb9b6ae249d29311808134f1