[blobfs-bench]: Avoid looping the rand_r seq

Previously for each blob, we were generating each byte from
the global seed, meaning that we consumed an element from the pseudo
random number sequence. This is O(#blobs * #bytesperblob) elements.

We reached the limit for 1MB blobs and 10k number of blobs. To avoid
hitting this, for blob we consume an element from the global sequence as
seed, and use a local pseudo random sequence to generate the entire
blob. This is O(#blobs) elements, thus the number of blobs to face this
issue is ~ 2^31.

TEST=blobfs-bench-tests

Change-Id: I46242b87af8536ee1f645407e3730c94d065df12

[compiler.h] Migrate many C++ clients of countof to fbl::count_of

The latter is safer in C++, and the former is a namespace violation in
compiler.h that eventually needs to be resolved.

Test: CQ; should be no functional change
Change-Id: I9809b9fe062fd5f07226323035bf094b3f9de798

[blobfs-bench]: Improve error logging.

Bot fails at this assertion, log the errno string with the assertion
fail.

TEST=blobfs-bench-tests

Change-Id: Icc2f0418a9f91fae3fc4a4663734fb93a0c5978f

[blobfs-bench]: Rewrite to use fs-test-utils.

The test now runs and measures operations at each stage. Instead
of measuring as it grows. This should provide a more fine grained view
of how the file system is behaving.

In essence:
Fill blobfs with up to X blobs, then measure Add one blob, read, write,
truncate and unlink. We repeat this multiple times to reduce noise. We
do this for various values of X.

Then using the data written by the api test, perform random reads.

ZX-2201 #done
ZX-2493 #comment

TEST=blobfs-bench-test

Change-Id: I7d0e0fb18e8324ed08ae6e13a9faf251ff313b50

[blobfs] Update benchmark to include negative lookup.

ZX-2192 #done

Change-Id: I52849a902a1c0808f06d12aa07bafad31d55f495

[blobfs] Benchmark cleanup

Update file style to be compilant with Google C++ Style guide. Mostly
naming and format.

Change-Id: Iea122950e93ace65a7a319891ae4000e8e93dbda

[minfs][blobfs] Update benchmark error messages

Change-Id: I77f0ed73e26cc42b20948391b5681c5c374a8b2d

[rtc] Update path to the rtc device.

The rtc device moved to the acpi bus.

Change-Id: I7fb65c8b863d3f58e7741d171253c62aea1c02b2

[minfs] [blobfs] Update benchmark mount paths

Change-Id: Ie73e190293dc0676a66def8d30c0dbe289bdcff5

[blobstore] Add asynchonous writeback queue

ZX-1312 #done

Change-Id: Ibc679148255b08e81e49a82e292917d0402d1b45

[blobstore] Rename blobstore to blobfs

Also, mount blobfs at /blob rather than /blobstore.

Change-Id: Ifdc473752ede37b909b30e35dbaac1397565a659