[automerger skipped] libprocessgroup: Use WriteStringToFd for WriteFileAction am: 1458350370 -s ours

am skip reason: Merged-In Id79f9e1095f52079393c58edb9a4d526f4cc6b5e with SHA-1 d4c53518fe is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/17061322

Change-Id: Ide30a97ae4fa54ce827c98b99987e92e2dbc498f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>