Revert RandomAccessFile to fsync/fdatasync for rws/rwd

Using O_SYNC/O_DSYNC may cause hard to detect performance regressions.
RandomAccessFile.write may result in multiple write syscalls,
O_SYNC/O_DSYNC flags will cause a blocking wait on each syscall. Replacing
them with single fsync/fdatasync call gives better performance with only
minor decrease in reliability.

+ updated 'android-changed' comments to cannonical style.

Test: CtsLibcoreTestCases
Bug: 37996859
Change-Id: I1fa15a4dcf895f483a8f4b18e244611d8b64e718