Add IsDynamicPartition API to easily check if a partition is dynamic am: eb9de16077 am: d14d6a20dc am: 6aa9432206

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1500611

Change-Id: Ia38b8a5e9ab05aa6ae39f3ee86cba438517bc870