[fs-management][minfs]: Add option to set min data slices.

Allows the FS to pre-allocate data slices when created, so it will have
a known minimum size, unless resized.

Add mkfs option to set the data slices, and a minfs option to reflect
this, so it can be propagated through fs-mkfs.

TEST=fs-management-test, fs-test

Change-Id: I3d774da9166d2949485709b913100c3113045fd3

[fdio] Move headers into lib/fdio/...

Change-Id: Ie8d74e716da913bf6e2672c4acf8cd67b4962b7f

[blobstore] Rename blobstore to blobfs

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

Change-Id: Ifdc473752ede37b909b30e35dbaac1397565a659

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[minfs] Make mkfs quieter by default

This makes the tests (which mkfs quite a lot) much
quieter.

This information can still be displayed with a "-v" flag to MinFS.

Change-Id: I6238ce60ad74babe9a76cdaa11ccce8707f494a6

[mkfs] Add support to CLI mkfs for blobstore

Change-Id: I93a76693a1a27a6c0dd4aacf7945533b69802f27

[fs] Use the countof() macro (for array sizes) in a few places

Change-Id: Ibf92282f039801dacf6ee646bee21dd4701cb217

[fs-management] Update FS libraries to share default 'launch' callbacks

In addition to consolidating 'launchpad' related code, this patch
provides three default 'launch' functions, which can be used alongside
the fs-management library:

launch_logs_sync - Kernel log + Synchronous subprocess
launch_stdio_sync - Stdio log + Synchronous subprocess
launch_stdio_async - Stdio log + Asynchronous subprocess

These functions are useful for an upcoming patch which makes the
filesystem test suite use the fs-management package -- it can use these
default launchers, rather than copying nearly identical code.

Change-Id: I7f1a846d8342821972f215d17ffbac4bdaad0260

[devmgr][fs][fs-management] Pass Block Device by fd, not path

Change-Id: Ie04ea7481edb6eb1375338666face5d14c7d879c

[signals] Remove legacy signal names

Change-Id: I6d4543358a16d16b9b9028ede06af40a632ba31b

[fs-mkfs] Add a 'mkfs' command which can format multiple filesystems

To use:
$ mkfs <devicepath> <filesystem>
Such as:
$ mkfs /dev/class/block/000 minfs
Or:
$ mkfs /dev/class/block/000 fat

Change-Id: Idc9c81b8bafc970817c1b882b87fad0d4914bfa3