Refactor the parsing of seinfo am: 7fd89c00f7

Original change: https://android-review.googlesource.com/c/platform/external/selinux/+/2836178

Change-Id: Ifa4dbb6ccaa95af13c388fb60736517b77b34475
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>