Merge "libsnapshot: Make the new Open calls look more like MapUpdateSnapshot."...

Merge "libsnapshot: Make the new Open calls look more like MapUpdateSnapshot." am: 9ec8c31a am: ef775977 am: d24bfd33 am: 52c8bd65

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1433352

Change-Id: I7d2c168af5ec4df29c7fcc0a90144a79c962b819