Sync file before using JournaledFile commit.

Ext4 doesn't guarantee that write file.new / close file.new
rename file.new to file will mean data in file.new makes it
to file atomically. The rename may happen with previous contents
of file.new and then later update to new contents
See docs for noauto_da_alloc
So rebooting the device during JournaledFile.commit may
mean we are left with an empty file.

Bug: 18590558
Change-Id: I35322c82871bed30c2c6ebbd1388338f0471f3ba