Change enum MustExist in CertUtils to IntDef integers

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

Change-Id: I5ebb52c86189f813db688e075ac8b2144d938102
4 files changed