Add a simple test to validate the filesystem APIs that connect the LK
filesystem layer and the virtualIO 9p devices. The test does the same as
`app/tests/v9p_tests.c` to mount the littlekernel codebase folder as the
`/v9p` on the LK filesystem. Then it tries to read the `LICENSE` file
under the codebase and show the first 1024 bytes of the file.
For example:
```
starting internet servers
starting app shell
entering main console loop
] v9fs_tests
0x80017060: 2f 2a 0a 20 2a 20 43 6f 70 79 72 69 67 68 74 20 |/*. * Copyright
0x80017070: 28 63 29 20 32 30 30 38 2d 32 30 31 35 20 54 72 |(c) 2008-2015 Tr
0x80017080: 61 76 69 73 20 47 65 69 73 65 6c 62 72 65 63 68 |avis Geiselbrech
0x80017090: 74 0a 20 2a 0a 20 2a 20 50 65 72 6d 69 73 73 69 |t. *. * Permissi
0x800170a0: 6f 6e 20 69 73 20 68 65 72 65 62 79 20 67 72 61 |on is hereby gra
...
```
Signed-off-by: Cody Wong <codycswong@google.com>
7cda17edfc