Vold: Add fsync in writeStringToFile()

Test: Build, test with ag/3180275
Bug: 68901441
Change-Id: Ieca9e5227025e00184a67508d5e8fbbddd12f21e
(cherry picked from commit 701d05d32c8b415c6fbb2e8c9439185333870046)
1 file changed