Use fsync instead of sync during first boot

1) fsync the specific copied file instead of sync whole file system
2) boost prio/ioprio for CFQ since cpppreopt is on critical path
3) change to foreground group

Before CL:
03-29 21:49:31.450     1     1 I init    : Service 'cppreopts' (pid 1662) exited with status 0 waiting took 55.175999 seconds
03-29 21:49:31.808  1440  1440 I PackageManager: cppreopts took 55591 ms

After CL:
04-01 15:47:43.841     1     1 I init    : Service 'cppreopts' (pid 1871) exited with status 0 waiting took 2.007000 seconds
04-01 15:47:45.343  1549  1549 I PackageManager: cppreopts took 3709 ms

Bug: 129542240
Test: boot
Change-Id: Ia9bacabe798764084790b077abc80ae60401f9c1
2 files changed