Add the utility functions to parse and validate XML files contains

public-key certificates for THM

Bug: 72524773
Change-Id: Iad30f11d14857bb919343b6a60b3b83cf85f2c52
Test: adb shell am instrument -w -e package \
com.android.server.locksettings.recoverablekeystore \
com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner