tests/9pfs: introduce local tests

tests/9pfs: introduce local tests

This patch introduces 9pfs test cases using the 9pfs 'local'
filesystem driver which reads/writes/creates/deletes real files
and directories.

In this initial version, there is only one local test which actually
only checks if the 9pfs 'local' device was created successfully.

Before the 9pfs 'local' tests are run, a test directory 'qtest-9p-local'
is created (with world rwx permissions) under the current working
directory. At this point that test directory is not auto deleted yet.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <81fc4b3b6b6c9bf7999e79f5e7cbc364a5f09ddb.1602182956.git.qemu_oss@crudebyte.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>