ANDROID: Incremental fs: Fix read_log_test which failed sporadically

Test failure was caused by drop_caches sometimes not dropping a range of
sectors in the middle of a random file. Fix by changing to reading the
file before we populate it, so the cache is not involved. Also by
populating it only on the last test, we test logging on both populated
and unpopulated files.

Rewrite the tests with the new test macros, and make the whole test far
more readable.

Test was taking 100 seconds to run, which was half the total runtime for
all the tests. This was due to the sleeps while reading. Reduce number
of such sleeps by a factor of 10, halving total test runtime.

Also incfs_test would exit with 0 whether tests failed or not. Fix.

Bug: 170104228
Test: Run incfs_test 100 times with -t10 -f4, and then again 40 time
      from end to end
Signed-off-by: Paul Lawrence <paullawrence@google.com>
Change-Id: I725dfdb44bf59ec9260230cb57781b2d0d31977d