Reserve space on disk using fallocate

There were crashes when android failed to extract
zip archives due to out of free space on disk, with stacks like:

  #00 pc 00000000000156b0 /system/lib64/libc.so (memcpy+176)
  #1 pc 000000000002e5b8 /system/lib64/libandroidfw.so
  #2 pc 000000000002f488 /system/lib64/libandroidfw.so (ExtractToMemory+328)
  #3 pc 000000000002f5c8 /system/lib64/libandroidfw.so (ExtractEntryToFile+268)
  #4 pc 00000000000287d8 /system/lib64/libandroidfw.so (android::ZipFileRO::\
  uncompressEntry(void*, int) const+12)

Space for the file is now allocated using fallocate rather than
ftruncate, since ftruncate dont actually reserve space on disk. When writes
to the mmaped pointer fails to be realized due to out of space SIGBUS
is the result. With this change we make sure that there is space available
before mmaping the pointer.

Change-Id: Ic5e8c33dbe729edb57919dacff73811b34cc2dc2