e2fsdroid: use libselinux function to read file context on device

When e2fsdroid runs on device, location of selinux file contexts
should be determined by libselinux instead of using arbitrary paths.

Bug: 35219933
Change-Id: I413b198422eddb212599498b532ba2c4d8bb36c6
(cherry picked from commit c0bd89b31a7719dd3d51137b3d47a9597ba6b038)
2 files changed