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

am skip reason: Merged-In Id79f9e1095f52079393c58edb9a4d526f4cc6b5e with SHA-1 e808841d72 is already in history

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

Change-Id: I7411b6d2e01d6758a0da438f705d405878b252aa